search doesn't show conversations after a specific date

When I use search in outlook, since two weeks it only show results before the 24th of March. The mails I received after the 24th do not show up in the search result, although they should show up because they have the keywords, or right recipients.

I tried several things: new updates, other search terms, different mailboxen but is is all the same in mij microsoft outlook app on my new macbook.

Can somebody help me? I use the search frequently while working.

thanks