I have reset the password, added 2FA, reconnected the Plex Media server to my plex accounts, all seems to work.
Issue i now have is when i log back on my kids smartphones (managed users), i log with my home owner user, and then when i want to switch user to go to their profile, i am redirected to the Login page.
I tried 3 or 4 times, same behaviour.
Prior to this security breach, i was able to switch between user without being logged out.
Bottom line: my kids cannot use plexamp with their own user login.