i've had a issue like this back in TBC i erased all my addons deleted the "Cache" & "WTF" folders then logged back online and it worked .

Cache - as the name says... its a cache folder that saves all item info like names and creature names so if you join a server and the rogue trainer is "Deathkight T10" delete cache folder and restart wow (Wont do any dmg)



WTF - Saves all configs like Video, keybinds addon configs (Wont do any dmg)