Does this happen when you launch Check For Updates from the Start Menu instead of inside the app?
If so, I don't know what this is other than it sounds like the update program can't reach sourcetreeapp.com for some reason. It might be your local firewall settings that are blocking it, please check your settings.
If all else fails, please just download the latest installer from http://www.sourcetreeapp.com, which will update your local install when run.
Supported Platforms macOS Sourcetree has a lot to offer and, like many developer tools, finding and using it all can be a challenge, especially for a new user. Everyone might not love ...
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