This issue doesn't occur at 4.21. It seems in 4.22 only. Bone is broken in the second SetAnimInstanceClass. It seems CurrentReadComponentTransforms doesn't update.
・Wait using timer without using delay node
・Without using parallel anim evaluation (a.ParallelAnimEvaluation 0)
TestActor in level move while changing AnimBP in SetAnimInstanceClass.
Crash on the third run.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-75188 in the post.