I've had a handful of these crashes.
crash-2022-04-20_16.50.00-server.txt
crash-2022-04-20_04.44.35-server.txt

the second one got so bad that it permanently locked down one of my test worlds. :V
but this is with version 2.0.2 in 1.16.5.

it seems to happen when a parasite begins attacking a mob that it just popped out of, hoping to multiply. the second one was when latching was turned on. But I had latching turned off during the occurence of the first crash, which just happened somewhere in the world when I was teleporting around inspecting some structures in my modpack.

The second one, which I observed which was actually some of the first times it happened, the parasites would attack zombies, but then the zombies would get staggered based on Project War Dance's mechanics which immediately after the loud CRACK would cause this issue. I've disabled parasites for now...

Apparently it's caused by this line?

Something about a reference to the mounted mob then invoking the reference again, which causes a crash if the mounted parasite suddenly gets dismounted?
Seems like this can happen at any point when the parasite kills something and gets dismounted that way, but just manifested itself earlier because they were knocking the zombies over with PWD's stagger mechanic resulting in their forced dismounting instead.