Sounds to me like a scripting error and your comment about loading then finding issue also lends weight to that. Have you been down the remove all (if can) and add back in each, test? If so you don’t say if without any it worked as that would lend weight to that theory of scripting issue with plugins.
Yes, I removed all plugins and thought I had added back all the minimum needed ones but seems like maybe I’ve missed a few. So I don’t think it’s a matter of a plugin conflict as much as a missing needed plugin.
Are groups and the forum dependant on a particular plugin?