exchange 2019 outlook 2016 search problem

[MandriNet]

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

[#2]

@MandriNet 

Hi,

Please rebuild indexing. Steps are as follows:

1. Close Outlook and open Control Panel.

   Note: Depending on the version of Office you're using, you might need to click the Start button, and on the Start menu, right-click Control Panel.

2. Do one of the following:

   • Choose Indexing Options.

   • In the Search box, type Indexing, and then choose Indexing Options.

3. In the Indexed Locations dialog box, under Change selected locations, select the check box for the location you want to modify, and then click OK.

4. In the Advanced Options dialog box, on the Index Settings tab, under Troubleshooting, click Rebuild.

   Note: A Rebuild Index dialog box opens warning that the "index might take a long time to complete." Choose OK to start rebuilding the index.

   Thank you,

   Regards,

   MD