In the last several days, three different people have been unable to open Source Tree until deleting this file the one that starts "SourceTree.exe..." I suspect the user.config file is getting corrupted, but just deleting that didn't do it. So maybe it's the Startup.Profile.
AppData\Local\Atlassian\SourceTree.exe_Url_yjhzxxhcu2ommegrdorjf3q1oqllqxiq\3.4.3.0\user.config
This is happening after a mandatory KACE reboot. I suspect there's a connection there, but the hardware folks deny it. Just happens to three people over two days, pure coincidence right. Oh, another demand for a KACE reboot, I'm nervous.