Endless password prompt for 2 Hosted Exchange 2016 accounts on MacOS

Im using 8.0.3494 on MacOS, and I’ve connected several accounts, including 2 hosted Exchange 2016 accounts (only mail, no contacts nor calendar).
Alternately, eM keeps prompting me for password and doesn’t accept it. Then it comes back to normal. If I force a diagnostics within the account panel, it does come back to normal, but only for 30min or so. Sometimes, clicking on the red triangle next to the account name helps, sometimes it doesn’t.
Any clues on how to solve this problem? Tried to read on close topics, but it didn’t really help me at this stage. Thanks in advance.