Alembic Import problem

Hi,
I’m just trying to import alembic animation cache with slots for materials. I got the slots to assign materials when I’m not using “Flatten Tracks” but then I’m not having the animation - just a static alembic. On the other hand when I use “flatten tracks” I have animation but only one material slot. What I do wrong? I’m using Maya and Houdini. Thanks. Kamil