I was browsing the Lounge and moused-over a thread to preview it. Nothing came up. Then I tried another thread and the 'preview box' just flashed on and off.

Then right after I noticed that I got this popup.



Now it seems the thread preview is just flashing on and off (box appears, stays for about a second, then goes away for a second, then appears again...) on virtually every thread.

 

Checked again... thread preview is working normally.

 

That's pretty weird. Let me know if it happens again, looks like nothing I have seen before.