Incorrect Velocity Calculation at Animation Sequence Transitions in Level Sequence

When adding an Animation Track to a Level Sequence and placing Animation Sequences back-to-back without gaps, the velocity can be miscalculated at the transition between sequences.

This issue occurs when a Skeletal Mesh uses an Animation Blueprint (ABP) and there is a difference between the output pose from the ABP and the pose specified by the sequence. In the Per Bone Motion Blur feature, velocity is expected to be calculated based on the difference between the previous frame’s pose and the current frame’s pose. However, at sequence transitions, the Skeletal Mesh internally reverts to the ABP’s output pose before immediately switching to the next sequence, causing velocity to be recalculated based on the difference between the ABP’s output pose and the new sequence pose within the same frame.

As a result, motion blur may appear around the Skeletal Mesh even when the character is completely stationary. Additionally, the incorrect velocity affects TSR, which can lead to noticeable artifacts such as jittering on the character's surface in cutscenes.

This issue occurs only when r.SkinCache.DefaultBehavior is set to 0. However, this setting is recommended for projects using MetaHuman, meaning that affected users may be unable to change it without unintended side effects.

Epic has only observed this issue in the Level Sequence preview within the editor, but a customer has reported that it also occurs at runtime.

To work around this issue, the following approaches are necessary:

• Disable Per Bone Motion Blur
• Blend between adjacent Animation Sequences
• Set the preceding Animation Sequence to Keep State

1. Download the repro project from the attachment.
2. Unzip and open the project.
3. In the Outliner panel, select NewLevelSequence and press Ctrl+E to open the Sequencer panel.
4. Lock the viewport to Camera Cuts in the Camera Cuts track.
5. Enable Show > Visualize > Motion Blur.
6. Scrub the timeline cursor.

Expected Result: Since the character remains completely stationary without any movement or animations, no Motion Blur should be visible.

Actual Result: Motion Blur is detected. When playing back the sequence, visual artifacts appear at sequence transitions.