Steps to reproduce:

1) Do interactive rebase of a branch on top of another. The branch can have one commit, but should have merge conflicts.

2) Resolve merge conflicts manually.

3) Continue rebase.

Expected behavior:  Rebase completed

Actual behavior: Sourcetree action hangs. You must cancel the action in the UI. See screenshot below.

Workaround: Quit Sourcetree, reopen it, and the 'Continue' works fine as expected.

Extra notes: This bug has existed for years, dating back to old versions of Sourcetree For Mac. It occurs 100% of the time for the repro steps. I have seen it on multiple computers, with different login accounts, and different repositories and upstream git repos.