Main panel works fine, Online players works fine, Banned players works fine.  Nothing customized in the plugin.  This only started happening as of last night and NOTHING has changed on the server other than our morning restart.  And yes I am using the most recent version of the plugin.  And I know for a fact this was all working perfectly last night.

This leads me to believe maybe a player name from the offline list is causing an issue?  I do not see any errors in my console.

Another hint is when I click Offline Players the entire GUI vanishes off my screen but my mouse cursor stays.  Almost like it is failing to render the Offline player list but is keeping the 'menu' open.  I have to click my hotkey for /padmin again to get things back to normal.  But if I click Offline Players it vanishes again.

Seems like a UI fail, indeed.
Could you please check the logs/RCON to see if there are any errors in there?
If not, please check the game client's console for an error message.

I have more clues for you now as I sort of fixed it ...

I checked my PVP server and it was working fine over there.  But my PVE server it was still doing that error.  So the only thing that could possibly have 'changed' on one server since last night when it was working fine is players.  Nothing else could be different.  So I started going through all the logins since I know I last used the /padmin last night and I only found one with special characters.  His name started with // so I kicked him (he was offline so would have been in that listing of /padmin) and POOF the menu works fine now.

Aha... Good to know. I shall attempt to think of a solution o7