[Forum] Thumbnails not displaying reliably

[bigrover]

We occasionally have thumbnails that do not display, instead what appears to be a generic broken link image is displayed. I have rebuilt the thumbnails, and moved the attachments from the database to the file system with no change in the frequency. I can cause the problem pretty quickly by going to the gallery and viewing the latest pictures. If I refresh that page I can see an error usually within four page refreshes. This is the same page, same images so I don't understand why it occasionally fails to display a thumbnail. It is usually not the same thumbnail that fails after more refreshes.

What should I be looking for to help resolve this problem? I am at a loss at this point.