Outlook keeps asking for Credentials

I know, the title seems like you might heard this a million times, yet, I have searched but haven't seen a similar issue or a solution to my problem.

In Outlook, I have 2 xxx@company.onmicrosoft.com accounts. Let's say Account A and B.

After configuring both accounts, for a while, all is fine and Outlook keeps the credentials saved.
But then suddenly it keeps asking for the Password:
Title: Connecting to A@company.onmicrosoft.com

ID: B@company.onmicrosoft.com  << already weird

Password:

Remember my credentials: clicked

Of course, I choose "Use another account", because it shows the wrong ID.

Now sometimes it asks for the credentials and showing the correct ID for the account it tries to connect to, but mostly it mixes up the IDs and can't even remember the correct credentials for each account.

System Information:

Windows 10 Pro / Win7 Pro

Microsoft Office 365 / Office 2019

The problem is, that we are also using vba macros to send or receive emails to either account and if Outlook can't handle 2 accounts, we may have to switch to another Email software.

Any Help would be appreciated.