most likely you need to adjust the end frame. I export with 25fps, also set up my sequencer to use 25fps, but Unreal seems to calculate a bit different. There is always a "" at the end of my frames, so instead of 100-250 it says 100-250.
If I simply remove the “*”, the post roll works like intended.
I use this all the time, its not broken, you just gotta check your import/export settings as well as the things I pointed out.
You can even retime alembics pretty well (if they don´t have changing topology).
But also, depending on what exactly you´re animating, alembic isn´t the best format to do so.
For simple transform animations, datasmith works just fine and is much lighter.
I use alembic ONLY for deformations or changing topology like fluid sims.