Threads no longer showing
 

On one of the forums where I provide a bit of tech assistance, suddenly since yesterday none of the threads are visible. The forums and subforums are there but if you click on a forum all you see are the subforums beneath that forum - no threads. You can get to any of the threads or posts via one of the search features.

Reverted all the templates - no change.

Switching to the vBulletin default style - no change.

Turned off the plug-in system entirely - no change.

Upgraded from 3.7x to 3.82 today - no change.

I'm guessing this is either a corrupted file or a bad template.

Any suggestions on where to start to troubleshoot this problem?