Outlook 2016 Instant Search not displaying all results for RDS users not in Cached Exchange mode

Instant searches in Outlook 2016 for our RDS users (not using cached exchange mode) are not displaying complete results.  If we search for mails we can see in the inbox from the past week, they do not display. As a test I connected to the RDS Farm and the same happens to me; when I switch to Cached Exchange mode--which we wouldn't do for the 150 RDS users--it works fine.

The button for Indexing Options under File - Options - Search - Sources is greyed out for everyone having trouble.
We do have the following registry key in place: HKLM\SOFTWARE\Policies\Microsoft\Windows\Windows Search PreventIndexingOutlook has a Value of 1.  I changed it to 0 and symptom persists.