No, we did not upgrade. Downloaded uddeim 2.8 and that's all we've used. However, at one time we deleted all of uddeim and reinstalled.
The messages that can not be erased seem to all be coming from the site admin. Some are simple PMs to users, others are "You have a connection pending..." so I assume the answer to your question is: both "user" (admin) messages and system messages.
Note* Actually that picture I attached didn't capture the indicator at the top of page (i cropped it out accidentally) where the cb login mod is located. you can see the "you have 2 private messages" blinking etc, yet all messages have been deleted.
When the user goes to their mailbox (mod_uddeim) via their profile where the mod is published in a tab, the messages are visible. one clicked, however, this message appears:
This message cannot be displayed.
Possible reasons:
You have no rights to read this message.
The message has been deleted.
Thank you.