I'm trying to report a nasty bug in Houdini 20. 
I load in my alembic that has animation. I apply all my groups and then use my materials. once it's lookdeved everything rendering nicely. I feel happy. Till I need to split things off, convert it, make a change, and merge it back into the asset. Example. My car tires weren't spinning, but I wanted to do that in Houdini, so the car as a whole moves in the alembic, and then I split the tires out, rotate them, and then merge them back into the rest of the car. when I add any transformation/movement all my Arnold materials no longer get recognized and Arnold will render it as if there was no material assigned. This happens no matter the order. If I do all the geo changes before or after the material assignment I get the same results. Broken materials. But if I remove those changes, and just DON'T touch the alembic, everything renders fine. Seems that if I move the geo node at the top, I get the same results, materials break. HOWEVER, if I add a null onto the geo node, and move that, things render fine. This isn't ideal. This wasn't a thing before. Houdini 19.5 would not break when I did the above approach. Baking out all my changes into a new alembic and bringing those changes back in, would work, and materials would not break. Again, it's not ideal. 

Houdini 20
htoa 6.2.5.0
Arnold 7.2.5.0