Outlook Not Responding

I have several computers in the organization running Outlook in which they get the message “Not Responding” when trying to open emails from the Inbox.  It may open two to three fine, but the third or fourth one stalls for 30 seconds or more saying “Not Responding”.  Searching the Inbox also stalls.

Here is what I have done to debug this.

1. Tested in Offline Mode.  No change.
2. Repaired OST file.  Reran in Offline Mode.  No change.
3. Repaired OST file.  Reran in Online Mode.  No change.
4. Ran Office 365 Full Online Repair.  No change.
5. Ran Outlook in Safe Mode.  No change.

The version is 2403 Build 17425.20146.

I search all over this forum, and did not come up with any answers.  Any help would be appreciated.