Unreal Engine Issues - Latest Bugs

Editor crashes in FAsyncLoadingThread2::ProcessLoadedPackagesFromGame when Level Blueprint references external actor

Adding a reference to an external actor in the level blueprint causes the package for the actor to be put in the import table of the level. In some cases, the actor package can end up calling postload before the levelinstance does, this ends up calling postload on ULevel which creates Upackages for all external actors in the level. These are added to the ConstructedObjects list for the imported actor. That actor now doesn't complete load until everything else in the level is loaded, at which point if one of the external actor packages has been destroyed null the editor crashes.

OFPA (One File Per Actor) is enabled.

UserSceneTexture not working in Virtual Reality

User reports that UserSceneTextures used in Post Process Materials are only correctly rendered inside the left eye in VR.

Adjusting Vegetation Growth for Bushes in Media Mode alters their global size settings

Reported in SF [Link Removed]

When making adjustments to the Vegetation growth Season parameter inside Media Mode, if a scene contains Bushes then any adjustments to the Vegetation growth will adjust the global settings for the Bushes' size.

Edits made in Media Mode should be restricted to the selected media and should not have any effect on the global settings for assets, and this requires manually tracking and readjusting the size parameters for all Bush assets when such edits need to be made.

Parameter metadata not accessible if modified in Material Instance and then converted to CustomPrimitiveData

There’s a potential issue with some changes we made to UMaterialInstance::GetParameterValue (https://github.com/EpicGames/UnrealEngine/commit/8f2bebb008ba645f5938da844cd46b0925322b13). It seems as though some parameters on an MI are returning False when they should be returning true, but only when the MI is converted from 5.7 to 5.8. If the parameter is created on the material in 5.8 he can’t reproduce the issue. Any thoughts here?

Report: Crash when adding new object instances in array in Widget Editor

Please review crash report from EPS case.

repro project attached

[Link Removed]

Custom expression additional outputs don't work when connected to World Position Offset

Custom expression additional outputs are considered (0,0,0) when connected to WPO.

The speed of Animators is increased in exports

Reported in SF [Link Removed]

When setting Animator tools to use Collision mode for video, the loop speed of the animator will be twice as fast as specified in the video export.

Attached a sample scene that demonstrates this behavior.

Unclear if this is a regression from 2026.1 to 2026.1 HF2. Last confirmed working correctly in 2025.2.

Translucent meshes randomly flicker when using VSM

Flickering can occur on translucent materials, usually in the distance when there is at least one directional light and when using VSM. Flickering seems highly dependent on framerate and timing.

Limiting the framerate with t.MaxFPS or turning off TLV batching usually seems to make the flickering stop (r.TranslucencyLightingVolume.Batch 0)

The flickering is from TLV only (not happening with forward translucent shading)
It seems it also happens without Lumen enabled
The issue may not happen with older Nvidia drivers, eg, 551.86
{{r.TranslucencyLightingVolume.Blur 0 }} doesn’t appear to affect the issue

This flickering issue doesn’t appear to be the same issue as the kind of flickering that can occur with meshes that intersect the edge of the TLV.

Additional Notes

r.OneFrameThreadLag 0 will kill it. And the render frame has to struggle (lag) for it to occur.
r.rdg.asyncCompute 0 might stop it, but only because the lag shifts a bit. You will still be able to get it with asyncCompute 0, but it just might be harder to reproduce.

Apply mesh paint Blueprint instance changes and save fails

After mesh painting on a BP Static Mesh Actor, and "Apply instance changes to Blueprint" the added virtual texture is removed with the log:

LogTexture: Display: Building texture TwoD: /Game/FirstPerson/Lvl_FirstPerson.Lvl_FirstPerson:PersistentLevel.BM_SM_MeshPaint_C_UAID_047BCBA595B946E702_1748064754.StaticMeshComponent0.MeshPaintVirtualTexture_0 (TFO_AutoDXT VT, 32x32 x1x1x1) (Required Memory Estimate: 1.271932 MB), EncodeSpeed: Fast
LogTexture: Display: Building texture TwoD: /Game/FirstPerson/Lvl_FirstPerson.Lvl_FirstPerson:PersistentLevel.BM_SM_MeshPaint_C_UAID_047BCBA595B946E702_1748064754.StaticMeshComponent0.MeshPaintVirtualTexture_0 (TFO_AutoDXT VT, 32x32 x1x1x1) (Required Memory Estimate: 1.271932 MB), EncodeSpeed: Fast
LogActorComponent: UnregisterComponent: (/Game/Blueprints/BM_SM_MeshPaint.Default__BM_SM_MeshPaint_C:StaticMeshComponent0) Not registered. Aborting.

If the apply step succeeds, saving the BP fails with the error:

"Illegal reference to private object: MeshPaintVirtualTexture /Game/..."

Rare crash in FWidgetAnimationState::OnStopped

The FWidgetAnimationState::OnStopped delegate is getting created when the widget anim state is being destroyed and then queued to be executed later. Something is happening between the queue and the execute, which means the OnStopped function is now stale.

Memory leak with -renderoffscreen and uncapped frame rate

A customer reported that -renderoffscreen leaks when running with an uncapped frame rate

'Use focal length' checkbox resets on reopening file

Crash when using ListStreamingTextures with VirtualTexturePrefetchMips

The ListStreamingTextures command causes a crash in FRenderAssetStreamingManager::HandleListStreamingRenderAssetsCommand when there is a virtual texture that uses crashes when encountering one of these textures.

It seems like the issue is that for VTs with VirtualTexturePrefetchMips, TextureMips is empty, so the OutputMipsString lambda needs to look in (*TexturePlatformData)->VTData instead to get the size of OutputIndex

Substrate Single Layer Water material fails to compile in blendable Gbuffer mode when using the Single Layer Water BSDF node

When using Substrate in Blendable GBuffer mode, a material with the single layer water BSDF node produces a shader compiler error :

MaterialEditorStats: Error: [SM6] Shader debug info dumped to: "\Saved\ShaderDebugInfo\PCD3D_SM6\NewMaterial_7d16ee4857da21e\Default\FLocalVertexFactory\TMaterialCHSFNoLightMapPolicy\0"

E:\Epic Games\UE_5.7\Engine\Shaders\Private\RayTracing\RayTracingMaterialHitShaders.usf(551,53): Shader TMaterialCHSFNoLightMapPolicy, Permutation 0, VF FLocalVertexFactory:

/Engine/Private/RayTracing/RayTracingMaterialHitShaders.usf:551:53: error: use of undeclared identifier 'GetSingleLayerWaterMaterialOutput0'

const float3 ScatteringCoeff = max(0.0f, DFDemote(GetSingleLayerWaterMaterialOutput0(MaterialParameters)));

MaterialEditorStats: Error: [SM6] E:\Epic Games\UE_5.7\Engine\Shaders\Private\RayTracing\RayTracingMaterialHitShaders.usf(552,53): Shader TMaterialCHSFNoLightMapPolicy, Permutation 0, VF FLocalVertexFactory:

/Engine/Private/RayTracing/RayTracingMaterialHitShaders.usf:552:53: error: use of undeclared identifier 'GetSingleLayerWaterMaterialOutput1'

const float3 AbsorptionCoeff = max(0.0f, DFDemote(GetSingleLayerWaterMaterialOutput1(MaterialParameters)));

MaterialEditorStats: Error: [SM6] E:\Epic Games\UE_5.7\Engine\Shaders\Private\RayTracing\RayTracingMaterialHitShaders.usf(553,39): Shader TMaterialCHSFNoLightMapPolicy, Permutation 0, VF FLocalVertexFactory:

/Engine/Private/RayTracing/RayTracingMaterialHitShaders.usf:553:39: error: use of undeclared identifier 'GetSingleLayerWaterMaterialOutput2'

const float PhaseG = clamp(DFDemote(GetSingleLayerWaterMaterialOutput2(MaterialParameters).x), -1.0f, 1.0f);

Crash when applying Decal material with Distance Cull Fade node to Decal Actor

The Editor crashes when applying a Material with a Distance Cull Fade node to a Decal Actor.

Fatal error: [Link Removed] [Line: 730]

Missing uniform buffer at slot 2, stage SF_Pixel. Please check the high level drawing code. Hashes: Vertex: 0412344381A54356369561A7263987C92AFDE647, Pixel: D5D063E9FD40319BC8B11C12936A2BA8DE6CA44A, Pipeline: 63E75D898B7658DB70F261F2CB6E568C0F398DE0.

AbilitySystemComponent::RepAnimMontageInfo causing push model validation ensure

When iterating through the struct’s properties to check if the values have remained the same, it seems as though the SectionIdToPlay has changed, causing validation to fail (see attached log snippet).

[StateTree] StateTree fails to transition to the next state in child states when parent state contains some tasks

StateTree fails to transition to the next child state in a tree where the parent state has a task such as Debug Text which does not influence state completion. The ST atttempts to transition from Level 1c which does not have a transition or next state and falls back to Root. This can be seen with Rewind Debugger or following the on screen text displayed. From an eye test, the ST should continue to go to the next state Level 2b.

Adding a Delay task instead will allow this to work if the delay is greater than that used in Level 2a. If you remove the task from Level 1c, it will also transition to Level 2b as expected. Adding an empty parent state to Level 1c with no changes in tasks also works.

Possible shader preload deadlock when using Zen streaming

The deadlock happens when enough shader preload are launch in parallel on a slower IO backend (like zen). When that happens, the preload starts a waiting period that never ends because it cannot be triggered anymore.

When the conditions mentioned in the Steps to Reproduce happens, the following happens:

GameThread eventually get stuck on FlushRendering

Workers (even including standbys when option is activated) and renderthread get stuck on FShaderCodeArchive::WaitForPreload

When going for the preload, an extra task that monitor the output of the IO completion event is created. The problem is that when the workers are oversubscribed, the extra tasks are never executed which cause the deadlock even though the IO for those preload requests are probably done.

See FShaderCodeArchive::WaitForPreload and FShaderCodeArchive::PreloadShader, the latter which create a FPreloadShaderTask with the read completion events from the storage as prerequisites.

Increasing the number of standby workers only delay the problem or in the case I studied did nothing at all. Disabling preload didn't seem like a great idea considering the slowness of zen storage (in comparison to straight SSD).

In the end, the solution seemed to be to bypass the prerequisites entirely and wait on the completion event directly (and the FPreloadShaderTask afterward). This enabled the tasks to work as intended possibly due to the task being able to run directly on the same thread during the wait period without having extra coordination through the prerequisite.

Nanite Landscape Visibility Layer Crash

Upon saving the level after creating the landscape and painting visibility, the editor crashes. When you restart the editor and load the level, you are greeted with a warning in the upper right corner of the viewport and a map check error that prompts you to rebuild that Nanite landscape. Upon rebuilding, the warning persists. If you then try to cook the level, the cooker crashes. Attempting to clear the visibility data using the landscape tool does not resolve the issue and upon clearing, if you then attempt to Save, the editor crashes with the attached stack trace.

The attached project has one level, NewMap, that has a landscape that is stuck in this state. If you attempt to cook, you should reproduce the crash.

When rebuilding the landscape, the following appears in the output log:

In UE 5.7:

LogLandscape: Warning: [NaniteDiag] ExportToRawMeshDataCopy produced 0 polygons for actor 'Landscape' (LOD=0, 64 components, polygons=0, 0 w/empty height, 64 w/visibility-paint, 64 w/visibility-data, 0 w/missing component-data, 262144 total height samples, 262144 total visibility samples, 262144 hidden visibility samples, 0 visible visibility samples, ExportBoundsSet=0, SkirtDepthSet=0).

LogLandscape: Failed export of raw static mesh for Nanite landscape (64 components) for actor Landscape : (DDC: 1, DDC read: 0 bytes, DDC write: 0 bytes, key: 7A6172126E32F37EE047EB5FEC99CA4692C4D92E, export: 0.030766 seconds)

In UE 5.8 the warnings are different but the Cook still fails. Upon closing the level the Editor crashes.

Custom Items and Inventory can appear enabled while actually being disabled

Toggling the Custom Items and Inventory setting and then closing the editor without saving can lead to a mismatch between the Project Settings Custom Items feature and the IslandSettings object in the world that governs behaviour in-game which leads to missing functionality. The project setting will look checked but Island Settings → Game Data → Use Custom Inventories will be unchecked without the ability to manually activate it.

WORKAROUND:

Unchecking and rechecking the Custom Items and Inventory setting will re-apply the change to the currently loaded Island Settings object. Be sure to save!