According to my game log, it's complaining about some copycat entity, but i couldn't get anything from that.
I think it's something related to Copycats+, but it's probably not because it crashed even if that mod was enabled or disabled.

EDIT : Another weird thing is that in the crash message, instead of Connected complaining, the create mod itself complains. The message shows up as just "null" so i don't think that's helpful.

EDIT 2 : The same thing happens with Copycats + too.

Are you using the newest version of Create: Connected? A hot fix for Create 6.0.6 was released not long ago.

I am. I'm using 1.1.7 and that's the latest version when installing on Prism.