When you morph into hostile mobs, and "ride" or "once ride" on a horse, ship, cart or other mods' chair, friendly mob start attacking you, you won't get hurt but the entity that you morphed on you will(and drop loots).

when you morph to other entity or disconnect when this happens, you'll leave a invincible&invisible entity there and friendly mobs will still trying to kill it until server restart.

and sometimes when those things happen, unload chunk and reload it; or close the game and rejoin will leave an entity which like #66 and it can be hurt.

mods used when testing:
forge-1.10.2-12.18.3.2477
metamorph-1.1.4-1.10.2
ShinColle-1.10.2.5.0 (also tested without it)

I'll look into that, but I can't promise this will be fixed. It seems like related to MC internals, and, boy, it's a very inaccessible and messy place.