The problem is native from the beginning and is still present.
We are in trouble with the search from outlook 2016 in online mode. We can find some results with a specific search query: (R: I: 2020 360-R: 20117- 1548GSC -A******** - Demande de pièce de rechange) * i censored some privacy info but searching for '2020-360' match all elements except for 2 specific items.
Refining our search query, including other texts that is part of the object of the mail, can find also the target mails. with the query : 'Demande' we find all the items requested.
We have verified the update level of the clients 2016, Office Professional Plus 2016 16.0.5095.1000 MSO 16.0.5095.1000 a 32bit
we have a new fresh deployed Server Windows 2019 with exchange server 2019 CU 7 onboard.
We tried all possibilities offered in this article: https://support.microsoft.com/it-it/office/risoluzione-dei-problemi-di-ricerca-in-outlook-2556b11f-f... In OWA we can find all items without problems, than we assume that Server side was fine. but We notice also that on Exchange console, with the command: Get-MailboxStatistics m********@a********.it | fl *funn*,*MCDB* we obtain some strange behavoirs: BigFunnelIsEnabled : True BigFunnelMaintainRefiners : True BigFunnelMessageCount : 16668 BigFunnelIndexedCount : 16002 BigFunnelPartiallyIndexedCount : 666 BigFunnelNotIndexedCount : 0 BigFunnelCorruptedCount : 0 BigFunnelStaleCount : 0 BigFunnelShouldNotBeIndexedCount : 1030