In accordance with CL-9139422 of [Link Removed], the SkeletalMesh ImportedBounds does not have an Extend operation. However, SBasePoseViewport, the UI for retagettes, continues to use ImportedBounds. So, the display is not correct.
To solve this problem, you can use SBasePoseViewport:: SetSkeleton needs to fix the following code.
The preview of SK_Mannequin_test in the UI for Retarget is not correct
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-94378 in the post.