[2019] Taking damage from invisible enemies, unkillable desynced enemies running through walls

Are you playing with mods? If so, please disable them to see if the issue persists.

Are you sure it’s not beastmen with spears hitting you from behind other bigger mobs. They have a long reach and are very annoying to fight.

As for flying enemies and so on. That’s normally caused by hosts with a bad CPU or a CPU that can’t keep up. Tell the host to lower his GFX settings.

It sounds like the “Player List Plus” mod and “Smaller network Packets” in network settings in game. That’s a well known bug that also produces the same problems that you are describing.