When a preview mesh is set inside the skeleton(see attached screenshot) and saved and an animation retargeted to that skeleton, the preview mesh you changed it to is not displayed on the animation.
Thumbnail is also incorrect
Does not occur/anim is based off of what is set in the skeleton in 4.18.3 but in this version the thumbnail did no update correctly
Expected: Animation defaults to display the mesh that is currently set in the skeleton when it is retargeted and the preview does not need to be changed twice
Results: Animation defaults to the other preview mesh and disregards which on is set in the skeleton when retargeted
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-59636 in the post.