10.8.1 Installer didn't terminate the existing instance correctly
Upgrading from 10.8.0 to 10.8.1 using the installer yielded following error:

After looking in the process manager, some residual instances of jellyfin.exe were still running, which prevented the installer from continuing. The tray icon was missing after the installer offered to shut down existing instance.
After killing the manually the installation completed.
Hrm, I don't believe we actually have any code in the installer to close the tray app or server process at all actually.
Edit: If it's running as a service it will stop it, but not in user mode. We'll need to add that.
Two related Reddit posts today of users that tried to update:
- https://www.reddit.com/r/jellyfin/comments/wi4ln0/error_when_installing_newest_version_of_jellyfin/
- https://www.reddit.com/r/jellyfin/comments/wi19b1/i_broke_something_updating_from_1080_to_1083/
Staring with 10.9, you do get a warning if Jellyfin is running, and the install will stop before anything happens.