Unreal Engine Issues
Unreal Engine Issues
Crash when a floor mesh is removed while a Vehicle has SimulatePhysics disabled
UE - Runtime - Simulation - Sep 1, 2026When SimulatePhysics is disabled, the constraint update is skipped, so a reference to an invalid (already-removed) particle is left behind. As a workaround, the approach suggested by the licensee — ...
Chaos: geometry collection with One Way Interaction never breaks from its own collisions
UE - Runtime - Simulation - Aug 21, 2026A geometry collection with One Way Interaction Level set to 0 never breaks from its own collisions. It falls, lands, and stays intact no matter what it hits. Set the level to -1 (feature off) and ch ...
Null FPhysicsActorHandle dereference in FBodyInstance::InitDynamicProperties_AssumesLocked when CreateShapes_AssumesLocked fails during async body init
UE - Runtime - Simulation - Aug 2, 2026Summary When CreateShapes_AssumesLocked fails during async body creation, the failed FBodyInstance is left in Bodies[] with a released actor handle. InitDynamicProperties_AssumesLocked is then called ...
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 ...