1. on the command line, check out a branch, but don't name it

git checkout origin/<sometopicbranch>

RESULT:

Note: checking out 'origin/<sometopicbranch>'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:
git checkout -b new_branch_name
HEAD is now at 605262c... formatting changes

2. Launch sourcetree from command line. Make sure the view setting is set to "current branch" and not all branches.

An error message will pop up "'git log' failed with code 128:'fatal: bad revision '(detached from origin/<sometopicbranch>)'"

This issue is similar to https://jira.atlassian.com/browse/SRCTREE-1292