I have the same problem as Casper. Windows app version is 5.11.0 and server is:
Mattermost Version: 9.0.0
Database Schema Version: 111
I can confirm there is an issue with that version of the windows app, i downloaded this older version and the problem is not occurring:
https://releases.mattermost.com/desktop/5.10.2/mattermost-desktop-5.10.2-win-x64.msi