In Beta 35.2, the dimensions were fixed for Cauldron servers. However, this might have caused some servers' GroupManager plugin to stop working in the LOTR Dimension. There is an article about fixing this here .
This fixed the problem immediately for me, and I hope it helps others as well.
Edit: In short, if you don't want to read it, just find this in your config.yml for GroupManager
# Worlds listed here have their settings mirrored in their children.
# The first element 'world' is the main worlds name, and is the parent world.
# subsequent elements 'world_nether' and 'world_the_end' are worlds which will use
# the same user/groups files as the parent.
# the element 'all_unnamed_worlds' specifies all worlds that aren't listed, and automatically mirrors them to it's parent.
# Each child world can be configured to mirror the 'groups', 'users' or both files from its parent.
# world2: (World2 would have it's own set of user and groups files)
# - users (World3 would use the users.yml from world2, but it's own groups.yml)
# - groups (World4 would use the groups.yml from world2, but it's own users.yml)
# - world6 (this would cause world6 to mirror both files from world5)
And change "world" (bolded and highlighted) to whatever the name of your world is.