Outlook for Windows "Not Responding"

I have searched this forum for a solution, and have not come up with anything.

Last week several members of the organization were getting "Not Responding" message at the top of Outlook when clicking on emails.  The user may be able to click on a couple emails with no problem, and they show up in the Reading Pane.  On the third or fourth one, Outlook stops responding.  The user has to wait 30 seconds just to read the email.  Also some users are having the same issue with search.

Here is what I have tried to debug this:

1.  Changing from cached to non-cached mode.  No change.

2.  Run Outlook in Safe Mode.  No change.

3.  Run Office 365 Full Online Repair.  No change.

4.  Run in cached mode, and Offline Mode.  No change.

5.  Repair the OST file with Scanpst.  No change.

6.  Run in Offline Mode with a repaired OST file.  No change.

7. Login to same account with OWA. No issues.

Strangely, not all users are affected even running the same Build number.

This is occurring on Version 2403 Build 17425.20146.

Anyone have any ideas to try?

Thanks!