Disappearing 365 Shared Mailboxes

I had and issue where O365 Share Mailboxes disappeared after a minute or so. After a bit of googling, I found this solution

Configure one of the following registry subkeys as follows:

HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\Autodiscover
DWORD: ExcludeLastKnownGoodUrl
Value: 1

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\x.0\Outlook\Autodiscover
DWORD: ExcludeLastKnownGoodUrl
Value: 1

Note: The x.0 place holder represents your version of Office (16.0 = Office 2016, Office 365 and Office 2019, 15.0 = Office 2013).

Taken from this MS Technote…..

https://support.microsoft.com/en-us/topic/after-migration-to-office-365-outlook-doesn-t-connect-or-web-services-don-t-work-3d9df009-597b-5d75-460c-4b7c64c833a1.