I've had to deal with this issue today and it seems that the Join button is the culprit. My user was getting stuck at Connecting when trying to join meetings with outside users. We tried uninstalling and reinstalling the app along with trying to use different computers. It wasn't until I tried to click the Join Meeting link in the invitation that the problem was fixed. It seems like the Join button that shows up on the calendar and in the invitation is faulty. Click the purple text that says Join Microsoft Teams Meeting and you should be able to get past the Connecting screen.
I've had to deal with this issue today and it seems that the Join button is the culprit. My user was getting stuck at Connecting when trying to join meetings with outside users. We tried uninstalling and reinstalling the app along with trying to use different computers. It wasn't until I tried to click the Join Meeting link in the invitation that the problem was fixed. It seems like the Join button that shows up on the calendar and in the invitation is faulty. Click the purple text that says Join Microsoft Teams Meeting and you should be able to get past the Connecting screen.