Update in Dec 21 broke my ability to sign in on the phone I've been using Teams on for the last 2 years, after freezing all messages to a particular date & I uninstalled it for the first time. Clearing cache & uninstalling/reinstalling multiple times has done nothing to help. Credentials are good, have it working on an older, defunct phone to test, just not on current one anymore. Don't know why. Was good, just now broken where I need it the most.