Well, the events are stored in the BBDD, so the events will come back as it was created if you dont delete from the database...
I will advise you to purge the events from database
I deleted all events in the database , when before uninstalling extensions
Try looking in the registry for the machines reporting these events
HKEY_CLASSES_ROOT\*\shellex\ContextMenuHandlers\DLP Manual Tagging
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\*\shellex\ContextMenuHandlers\DLP Manual Tagging
Could be hard coded into the registry still or in the document properties....it appears the computers are not getting the new policy or cant delete it.
I would try deleting all the .opg files on the computer if that is the case.
Ensure that the incident reported shows the latest policy. If the machine did not receive the latest policy where the old tag was removed it will still be reported back.