Pb: unknown activities in reports

How did the user delete meetings ?
From meeting screen or directly in the database ?

Please check in table planningelement for lines referencing the meetings : refType='Meeting', refId=id of meeting.
Delete these line if they are found.

New information: An user have deleted two meetings, with real time

It should not be possible to delete meetings with real work.
I am interested to know how your user succeded in deleteing the meetings with real work : I tried but could not.

To fix your data, you must :
- retrieve lines in work table corresponding to work on the meetings : they should be line with refType='Milestone' and 'refId'=50 or 51.
- identify assignement linked to these work lines (idAssignement)
- delete work lines
- delete assignment
- update project : to have real work values updated.