The "Couldn't look up profile properties" error was caused by the plugin attempting to look up "player->" heads because Mojang limits the number of requests the server can make within a certain timestamp. For this reason, the "player->" heads are disabled until I find a solution on how to fix them. "custom->" heads are still working as intended.
BUG FIXES
Fixed: Some menus freezing the server.
Fixed: The "Couldn't look up profile properties" error.