This certainly should not happen, it's a zombie-trigger

Maybe there's still another such trigger somewhere. Try to remove all media session changed triggers in all flows and delete them in the maintenance window then close Automagic using the back key. Reboot the device once and check that the trigger indeed does not exist anymore in the list of triggers or in the maintenance window.
Does the notification still show up now? If yes, please enable Debug Log, reboot the device again, wait until the notification is shown again and then send the log to me (menu->Manage->Log, menu->Send Log), please also include the flows.
Did you do anything special when creating the trigger or did you just manually add it to a flow and then remove it again?
Thanks & Regards,
Martin