AutoSize triggers ensure on shortened Skel Anim Section moved past anim length

In Sequencer, calling "Edit > Auto Size" on a UMovieSceneSkeletalAnimationSection triggers the LowerBound > UpperBound ensure in UMovieSceneSection::SetRange (MovieSceneSection.h:333) when the section has been shortened below the animation length and then moved so that its start frame is beyond the animation length.

Root cause is in UMovieSceneSkeletalAnimationSection::GetAutoSizeRange (MovieSceneSkeletalAnimationSection.cpp:337). It calls InnerToOuterTransform.TryTransformTime(InnerEndTime).Get(InnerEndTime), and when the inverse transform fails to map InnerEndTime to an outer time (because the value is outside the Inner Clamp or Inner Loop range), the .Get(InnerEndTime) fallback returns the raw inner-tick value. That value is then used as if it were an outer-tick value in GetInclusiveStartFrame() + (OuterEndTime - OuterStartTime).FrameNumber, mixing inner-tick and outer-tick values and producing a negative or otherwise invalid length. SetRange then refuses the range and Auto Size has no effect.

This behavior was introduced by CL 40829088 ( [Link Removed] Closed , fixed in 5.6), which replaced the previous TOptional check with a .Get(fallback) pattern.

1. Open a new LevelSequence.
2. Add a Character actor and assign a skeletal mesh that has at least one animation available.
3. At frame 0, add a Skeletal Animation Section using any animation.
4. Drag the right edge of the section inward so the section length is shorter than the animation length.
5. Drag the section body to the right so that its start frame is greater than the animation length, keeping the section length unchanged.
6. Right-click the section and choose Edit > Auto Size.
7. Observe the ensure failure in MovieSceneSection.h:333 and that the section length does not update.