Mail app emails not viewable when selecting a second installed account

When I open the mail app I can see all my accounts and see how many new emails per account (Capture 1).


If I then go to the second account it shows no mail (capture 2) even though I know there are emails in the inbox.


I then go back to the first account and that also shows no emails (capture 3).



If I then close the app and reopen it, it takes about 5 mins to open and I have the same initial issue (capture 4).


I have the same issue on two separate systems and have tried to uninstall/reinstall but, when I do this as soon as I add a Gmail account I have the same issue.

Is this a known issue?

Mail app Version 16005.13426.20688.0
Window 10 Pro Version 20H2 (OS build 19042.906)

Not that I know of, as my Outlook/Hotmail and Gmail Accounts work properly, along with 4 other Mail Accounts, and has done for 5 years, all IMAP.

I would check the Sync and Inbox setting options for each Account in the Mail App.

Also use the Webmail access to check what options are set in each Account, Outlook and Gmail have fancy sort options which they have a tendency to switch on when they change the feature set.

The Mail App takes < 2 sec to load, ~5 sec first one of the day, with a standard Laptop HDD. One of the few background Apps running.

I would also run the usual SFC, DISM servicing stuff and the Apps troubleshooter.