Have you tried putting them back, one plug in at a time?
Next on the the list but as this is a production server I have to wait until tonight when my users go home. :)
Something I didn't note before is that this is a new deployment. I rebuilt the server from scratch on July 7th-ish. There's a hole in the event log stating July 30th until August 3rd when the server had it's weekly reboot. At that point the plug-ins stopped loading. I was on vacation and nobody really noticed until now. :/
Remove all plug-ins, attempt to add one at a time. With even one plug-in in the extensions folder the Admin console shows all four, each duplicated. Suspecting something is up with preference, or configuration file now.