And some new informations......this occurs right now on one of my project.
I input real work allocation to a user for an activity (Act A).......the input is correctly took into account....but there is too an other real work allocation for the same user on a other activity (Act B ) that appears

(real work I did't input)
When I go to this concerned activity (Act B ), I see real work and a real date (23/12/2106) : a few second before, there was no date !!! (my project has a start date on 25/04/2017 and absolutly no activity start before this date.
When I go on real work allocation screen, on the 23/12/2016, for the concerned ressource, I didn't see any real work input (I saw others week, before, and after, since today, and no real work appears.
If I use report to see "workload by ressource / annual", there is no workload for 2016, and no workload for 2017 for the activity Act B.
I can't supress the "false" workload input because it's doesn't appear.
I really don't understand anymore what's happend.
Can you help me ?