Hello Fabrice,
Thank you for your explanation. I will definitely try membership management via AD Group.
Fabrice> If there are AD Users that do not appear, it could be they are located into OU that are not readable by default by any Users?
Both shown and not shown users are from the same OU... This is not an OU read issue. And our AD is single domain.
I had no time to play with it yesterday. And when I open Admin Portal today I can see all the users appear. Very strange. It somehow solved itself. I would like to know what causes such a delay for some AD accounts? Any idea?