Perhaps the names have been changed to protect the innocent.
Caching is based on URIs, and if the URI changes (e.g., due to a file name change on the server), the visitor's browser doesn't see it as cached. I suppose it could also be a shift from HTTP to HTTPS or something screwy like that (which would also change the URI), but I can't imagine using HTTP in this day and age.
The Xenforo Security add in that caused the issue yesterday has been updated as there was a bug which caused the issue we and others running it had.
The author has recommended uninstalling the old one and installing this version fresh. So I will be doing that.
It should not slow us down, we were running that add on for a long time but yesterday update had the bug when it was trying to do its daily maintenance.