Alembics only work if the start frame is zero during import

I have a very long cloth sim (8000 frames). I have broken up the simulation into 1000 frame chunks. So I have several cache ranges( 100-1000, 1000-2000, etc. ).

However, when I import into unreal and use the cache in/out range, the cache is screwed up.
After experimenting, I turns out I always have to import with frame 0 as the start frame or the Alembic doesn’t work. Skipping empty frames doesn’t work.