Heyho,
For some reason the newest version (10.1.1) crashes for me and my friends. It happens with basically any morph, even with the demorph command. Crash log here: https://pastebin.com/0pKpZ08E
The crash seems to be client side only.

Upon further testing, with just Morph and IchunUtils installed it does not happen, hence I assume its because of some interaction weirdness.

Playing on a server, optifine is not installed. It also happens on Singleplayer on any morph, crash log for executing a demorph command as a player here: https://pastebin.com/cpwUGx0u

I'll be happy to provide any other information you need!

If you'd like, report the issue to the mod pack creator so they can update the pack as well.

Also: Thanks for the way you've made your issue report, detailing what causes the crash and including the crash log goes a long way for us devs to figure out what's going on. Bit refreshing to see!