FYI tasks not clearing from user worklists

Users have increasing been reporting that older FYI notifications are no longer clearing from the worklist and BPM bell icon. I have attempted to recreate the administrative profile option FND_NOTIFICATION_EXP_PERIOD and we also run the synchronization process, but tasks remain. I noticed that many reporting recent transactions having this issue and going back as far as May transactions so I'm wondering if it isn't tied to our May upgrade somehow. Has anyone else seen this, or know of other settings that may control how these are cleared?

Thanks,

Jon