Checking full access permission on mailbox

Hi all,

I'm currently doing a migration from Notes to Exchange Online.

I did one this morning and all went OK, however trying a migration now for 7 mailboxes and the bit right at the beginning where it says "Checking full access permission on mailbox" has been sitting there for 20 mins now where as it usually takes 2 seconds per mailbox. 

Checking the Microsoft 365 admin centre Service Health shows an issue:

"A very limited number of users may intermittently be unable to access Exchange Online via any connection method" which started on August 26th !

Any ideas whats going on?