When importing an Alembic file as a Skeletal, the animation and morph targets keys are there but when played in the Viewport or Sequencer there is no animation.
This was reported and tested in 4.20.1 (CL-4233996). This issue was reproduced in 4.19.2 (CL-4033788) and Main 4.21 (CL-4302610)
Results: The animation doesn't play
Expected: The animation plays
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-63183 in the post.