When importing an animation using the same import settings as the imported skeletal mesh it is meant for part of the mesh is rotated 90 degrees around the root. The files that were used to verify the issue are attached (1 skeletal mesh and 3 animations).
Found in 4.15 CL#3450819
Reproduced in 4.21 CL#4753647 , 4.22 Source (from GitHub)
1. Create a clean project from the Epic Launcher.
2. Import a skeletal mesh that has animations built for it in separate fbx files with Convert Scene and Force Front Axis set to True.
3. Import an animation fbx associated with the skeletal mesh with Convert Scene and Force Front Axis set to True.
4. Create an animation blueprint for the skeletal mesh (right click->Create->Anim Blueprint) and use the imported animation for the Final Animation Pose.
5. Place the skeletal mesh in a level and set the Anim Class to the animation blueprint that was just created.
6. Simulate the game and observe the animation.
Results: The animation has parts of it rotated 90 degrees around it's root.
Expected: The animation is oriented the same as the skeletal mesh it is based off of.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-77046 in the post.