My computer was sleeping for a couple of days and had no internet connection. When I resumed it had the error message as shown in the attachment and no way to recover from it even after connecting back to the internet. See video. Eventually had to Force Quit to get past this issue.
Seen on Mac Desktop 18.104.22.16879
1. Open Mattermost Deskptop on Mac.
2. Leave computer to sleep and remove internet connection.
3. Wake up computer
4. Connect back to the internet.
5. Go to Mattermost window.