Problem: I had a considerable amount of changes pending to be committed. When I tried to commit some of by blocks (a block at a time) eventually, source tree stopped working (the loading spinners were shown and the user interface was not responding). I’ve tried to fix this issue by closing the application entirely, that didn’t work, source tree was not responding after a few seconds of re-launching the application.
Beware, you will lose your uncommitted changes so backup your important changes , or commit them using your IDE if supported.
Worked for me.
Hope it helps someone.