Importing an Alembic File with "Skip Empty Frames at the Start of Alembic Sequence" Enabled Causes Crash.
Found in 4.20 Preview 5 CL# 4173640 and 4.21 CL# 4207835
The engine will crash
The alembic file would be imported
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-61761 in the post.