Unreal Engine Issues
Unreal Engine Issues
Non-determinism in StaticMeshComponent::BodyInstance when cooking LevelInstances
UE - Runtime - Simulation - May 21, 2026A licensee reported that serialization of LevelSequence with StaticMeshActor with default collision for which mesh has NoCollision profile is not deterministic. The issue seems to be in the fact tha ...
Meshes with scaled root bones pop when entering simulation
UE - Runtime - Simulation - May 15, 2026This issue is fallout from the changes in 33851494. Prior to that, we didn’t get the pop on beginning the sim. The problem appears to be that in USkeletalMeshComponent::PerformBlendPhysicsBones we ...
Physics Constraint Actor: When plasticity is enabled, Drive Position Target is reset to zero on constraint initialization
UE - Runtime - Simulation - Mar 5, 2026When a Chaos joint constraint is first created, having linear/angular plasticity enabled will unexpectedly force its linear/angular drive position target to zero on initialization, disregarding the ...
Division by zero causing NaN/Inf on USkeletalMeshComponent::UpdateRigidBodyScaling() when setting scale to zero and back
UE - Runtime - Simulation - Feb 11, 2026Up to UE 5.5, skeletal mesh physics did not get updated when the component's scale changed. This was improved on January 2025 with CL 39190335, which addressed [Link Removed] ...
StaticMesh reimport not preserving support for physical material masks
UE - Runtime - Simulation - Feb 10, 2026Client has a workflow issue with the reimport pipeline: UStaticMesh::bSupportPhysicalMaterialMasks should be copied over to UBodySetup::bSupportUVsAndFaceRemap before it takes effect for raycasts, ...
bWeldSimulatedBodies not replicated with attachment
UE - Runtime - Simulation - Jan 13, 2026The bWeldSimulatedBodies attachment parameter is not replicated to clients, both in USceneComponent's attachment replication handling and in AActor's FRepAttachment struct. If AttachToComponent is c ...
"Scale for <ComponentName> has a component set to zero, which will result in a bad body instance" warning spam when moving actor instance even with Collision Profile overriden to "NoCollision"
UE - Runtime - Simulation - Jan 12, 2026When a StaticMeshComponent has a scale component of zero in WorldSpace (after accumulating with the hierarchy from the root to it), function UPrimitiveComponent::OnCreatePhysicsState() logs the warn ...
Unable to interact or collide with geometry collection after Removal on Sleep or Break timer finishes, yet unbroken piece continue to render
UE - Runtime - Simulation - Dec 18, 2025Context: A static mesh is able to have a geometry collection generated from it using the Fracture editing mode. It can be fractured in many different ways, and when acted upon by a chaos field agent ...
Convex hull generation fails when first 3 verts are colinear
UE - Runtime - Simulation - Dec 9, 2025The licensee identified a number of cases where loading assets will trigger convex hull generation warnings:If the first 3 verts in the set are colinear (in which case IsPlanarShape() returns true b ...
Chaos sometimes can not generate contact points while two dynamic convex hulls actually collide. It results in instability in the contact behavior - such as jittering, inconsistent contact forces, or unexpected collision responses.
UE - Runtime - Simulation - Dec 2, 2025Context: Chaos Physics is able to use convex hulls to represent object collision geometry for queries and simulation. Problem: Chaos sometimes can not generate contact points while two dynamic conv ...