Released: April 2021 Exchange Server Security Updates

    Anyone actually have a success, without these issues or are they constant? Can anyone note what they may have done differently in this post to install and make the install success without these issues? We are planning on upgrading to CU19 over the next couple of days on our 4 node cluster. Then we will install the security patch pending any workarounds for ALL the issues found in this blog.

MICROSOFT: Your assistance would be appreciated here. You have many Exchange admin's frustrated and worried about the install of the patch. 

NOTES:
-Related to CU19 vs CU 20, doesn;t seem to matter. These issues occur on each.
-I think we all know now to install via Elevated cmd
-Edge servers need the patch as well
-If on CU19 and you install the patch, and updating to CU20, the CU20 paytch will need to be installed. = Nino Bilic

Seems pretty consistent, this patch created problems in the following areas

1. FreakyNL = If $ is in the Username = "Copied my admin account to one without $ in the names - problems be gone"
2. FreakyNL = "Admin account (only have one w/o a mailbox here I'm afraid) on either /owa or /ecp throws 'Cannot serialize context'" Seems to be if the Admin account doesn't have a mailbox. Arbitration mailbox has been mentioned as a potential.
3. FreakyNL = "Start exchange management shell doesn't work" Not sure if this is specificly because the admin account has a mailbox
4. Multiple people with Exchange Toolbox issues as well. .NET assembelies have been mentioned = FreakyNL
5. GregS410 = "something is up with the ability to remotely monitor Exchange 2016" Seems to affect many monitoring products such as PRTG
6. Prashant_A-Rookie = ECP issue may be resolved by https://docs.microsoft.com/en-us/answers/questions/116565/event-id-1310-aspnet-40-exchange-2016.html. Anyone else try this?