Sitting and sneaking mods could be compatible with this. For now the player just bugs out.

Something to do with the pack overriding the leg animations. Happened to me too and I'm pretty sure they're working on it (at least I hope so)

Some of the limitations I have with the resource pack is that I can't stop the legs from overwriting animations without getting rid of the fancy walking animation. I tried to go some steps in v3.0 but it started to cause issues with the body so I had to archive that version and retire that feature in v3.0.1. I may try to do it again some time with a different method.