I currently have 3 tamed ferrets from the Critters and Companions mod that aren't healing like they should. This might be a specific issue on the other mod's end, but here are some of the issues I'm finding:

• They don't heal on their own, or when I feed them (they prefer rabbit meat) and instead go into love mode.
• When I applied the Extra Health enchantments on their collars, the total hearts increase but the health stays at the halfway point.

There may also be a conflict with the ClassesMC mod where I have the Ranger class which let's me auto-heal tamable mobs.

I have not tried to use the collars on vanilla mobs.