I am having the same exact issue. Our irganizatuon recently changed its name and thus out UPN. After that j had to sign in again. That wasn't working, same issues described here. I then uninstalled several times. I tracked down every file and presence file and deleted them. Restarted, repaired permissions, and reinstalled. Same problem, it gets stuck "loading".
If you tell me how, I can send my log data to you.