For some reason my represent button does not appear on groups and yes they are public ones. Its only the report button in the top right corner and I dont know how to get it to appear again. I tried signing out and sigining back in, restarting vrc and my headset but whatever I do it just wont appear.
I noticed this behaviour happens when viewing groups from your profile. When viewing them from the dedicated groups tab though, the Represent Group button is there.