When importing animations with numeric names from fbx in UE5.2 or later, the AnimationSequence asset is created but the animation data is not imported. The workaround is to not prefix bones with numeric names. This is a regression because it worked in UE5.1.
1. Import skeleton from fbx with bone names starting with a number
2. Import animation from fbx with bone names starting with a number
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-191527 in the post.