This is Exchange 2016 On-Prem. Outlook 2016, and 2019 for sure. I know I'm posing in the cloud forum, but there is no On-Prem Exchange category any longer. The common issue? 30 seconds after clients open Outlook, about the time the email/alert notification window pops up, the Public Folders and all shared/deleted mailboxes disappear. Before they disappear, they are accessible, and work properly, then POOF, gone! The usual fixes that don't work (or work for a day or two)? Repair Office, delete and recreate the outlook profile, repair the OST, un-check the download shared folders, switch to online mode (turn off cache), run Outlook in Safe Mode. We also created new public folders and verified they also fall to this issue. I have open a case with Microsoft at the tune of $500. Case number 24155972. Microsoft has been a NO SHOW on this issue. Occasionally chiming in to ask the same 5 questions. Apparently Hafnium has been keeping them busy. So our issue is small potatoes. They have spent some time on it, remoted in, took some info, played around with it, and agree it is baffling as they could not fix it so far. SO it is not the obvious answers. This is an elusive issue. I need the true guru answer here. This server has been running flawlessly for 3 years, then on February 4th, users began having the issue, not all at once, not all on that day, but within a week everyone had eventually had this issue. We find the most useful fix is the recreation of the Outlook profile, it will often bring the Public Folders and Shared Folders back for a time period of a few hours to a few days. We have spent 40% of our time deleting and recreating the profile so people can work. I do not believe it was an update, the last updates to run before this began was a solid three weeks prior. We even applies the latest CU19 in order to try to solve it. I install LOTS of On-Prem Exchange servers, thousands of end users with Outlook Desktop Application. This issue is only happening with one client server and its 75 users. This leads me to believe it is a server issue, but I cannot track it down. Half of me believes Microsoft has boobietrapped the server in hopes we'd make a move to migrate it all to Microsoft 365. I'm reaching out to everyone else because this needs fixed, and as much as I know about Exchange configuration and management, I cannot put my finger on what's happened here. One of you has the magic pill. Please help.