There's a community report here: https://forum.mattermost.org/t/client-stuck-on-startup/7016
and Ian reported "iOS, iOS Classic and mobile web MM are all disabled for me. I can’t load iOS and the send button is broken on Classic and Mobile Web."
Potential steps to repro:
1. Enter server URL
2. Click connect
3. Login options are shown
4. You select email/password
5. It takes you to input your credentials
6. After entering username/password you get prompt for MFA
7. Enter MFA
8. Loading screen is shown
Observed: No channel is loaded
No testing required.
See comment below. While there was a PR that fixes an issue that may be contributing to this, I was unable to repro the issue.