Hi Robert, 

I'm sorry you're having trouble with your MAPI accounts. I'm going to start a support ticket so we can look into this issue. 

Hello,

We just released a new BETA with some additional MAPI fixes. We had some notification changes that should resolve issues with folders not getting updates. With this release we are recommending people start fresh with their MAPI tests, deleting your Outlook profile, and deleting the MAPI/EWS entry in your connectivity settings in webmail user settings. You can use this guide to help clear out older information,

The newest issue, where Outlook stops syncing, and restarting Outlook fixes it, I can confirm is fixed.

The original issue, where for some inexplicable reason Outlook stops sync'ing entirely, and the only way to fix it is to clear the offline cache or delete the OST, is not fixed.

I deleted and recreated the Outlook account as well.

We've started seeing this too. I have 2 folders with unread emails in them that Outlook is not syncing any more. Even with restarting it. mapi logs have nothing to say in terms of exceptions. 

@EchoDreamz We are experiencing the same issue.  Latest Beta from Friday V7419 and experiencing Sync issues.  My Outlook 2019 stopped syncing last night at 10:42 all of a sudden.  I do have some errors though so I am going to open a ticket.    

Looks like the system things we are out of disk space and an exception related to Contacts.

Something else that I see that may be related is that I am asked every 5 to 10 minutes to sign in again.