We use MS Teams in work and after using it for close to 12 months it really has won us over from Skype. It did take a little bit to get used to the idea of 'conversation threads' and not just random chats but once you get used to it, you'll never go back
However, there is one issue that a few of us have run into where Teams would just keep showing the 'Logging you in' modal when starting up after we change our system passwords. This would happen even if you logged out of the current Windows session or rebooted the PC.
The solution to this is to go to the Taskbar in the lower right and find the Teams icon. Right click on it and select the 'Logout' option. This will then close down the current Teams session and open it up again but this time it will prompt you for your username and password so you can enter in your updated password.
This doesn't happen every time your system password is updated so I'm not entirely sure what causes this session issue but at least the fix is nice and simple.