After setting up a Virtual Bone on the skeleton and having it drive a Skeletal Control Node in an Animation Blueprint. Reimporting the skeletal mesh will cause the setup in the Anim BP to revert back to its default setup.
This was reported and tested in 4.21.1 (CL-4613538). This was reproduced in 4.20.3 (CL-4369336) and Main 4.22 (CL-4670176)
Results: The skeletal mesh in the Anim BP reverts to its default position
Expected: The skeletal mesh in the Anim BP doesn't change after reimport
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-67906 in the post.