Lags in animation when set leader pose component is used

https://udn.unrealengine.com/s/question/0D54z00009UJv5HCAT/lags-in-animation-when-set-leader-pose-component-is-used

From licensee:

"USkinnedMeshComponents have the option to double-buffer their bone transform data, and UE5.2 changed when the buffers are swapped. Previously it would happen during the PrePhysics tick (e.g. inside USkinnedMeshComponent::FlipEditableSpaceBases()), but now it occurs during the parallel end-of-frame render data update (downstream of USkinnedMeshComponent::SendRenderDynamicData_Concurrent()), which happens concurrently for all relevant components. This means that on some frames, some of the pose-follower components may be processed before the pose-leader, causing the follower to use the previous frame's bone data because the leader's buffers haven't yet been swapped.

We do have a tentative fix, namely separating out pose-loader components (USkinnedMeshComponents with "GetFollowerPoseComponents().Num() > 0") into their own array, instead of placing them into UWorld::ComponentsThatNeedEndOfFrameUpdate. Then inside UWorld::SendAllEndOfFrameUpdates() we fully process the pose-leader array (using an adapted version of the "ParallelWork" lambda) before processing the original array. This looks good in early tests and we're in the process of vetting it more thoroughly."

Also reported by another licensee: https://udn.unrealengine.com/s/question/0D54z00009RFRzOCAX/skin-cache-and-setleaderposecomponent

This is a race condition, I am only able to repro it by artificially staging it by messing in code.