Layered Blend Per Bone nodes evaluate to 0.0 weight with Blend Masks when s.AsyncLoadingThreadEnabled is active in Editor

When starting the Editor, Layered Blend Per Bone nodes using Blend Masks inside dynamically linked Anim Layers completely ignore the blend pose (evaluating to 0.0 weight for all bones). Disconnecting/reconnecting and recompiling fixes it for the session, but it breaks again on the next Editor boot. This does not happen if s.AsyncLoadingThreadEnabled is disabled.

By debugging the engine source code, we caught the exact moment of failure. During the asynchronous loading phase inside FAnimationRuntime::CreateMaskWeights(), the pointer to the UBlendProfile asset is not null, but we inspected its object flags:

BlendMask->HasAnyFlags(RF_NeedPostLoad) returns TRUE

BlendMask->HasAnyFlags(RF_LoadCompleted) returns TRUE

FLinkerLoad::CreateExport()
FBlueprintCompilationManagerImpl::FlushCompilationQueueImpl()
UAnimGraphNode_LayeredBoneBlend::ValidateAnimNodeDuringCompilation()
FAnimNode_LayeredBoneBlend::RebuildPerBoneBlendWeights()
FAnimationRuntime::CreateMaskWeights()