Reported to the issue repository over xJon/Hexxit-II#46 by multiple users.
Any idea what's causing this?
Thanks!

It is possible server is not properly syncing the animation state of the golem to clients. Sadly, i don't support 1.12 anymore, so any investigation into the matter would have to happen by someone else.

Hey @AtomicStryker, thank you for the response. It ended up to be a mod incompatibility which was resolved :)