Unable to use "Check out in SourceTree" option

In Jira, I need to create a branch for a task. That takes me to bitbucket, where the branch is created and I get an option to ...

```
Check out your branch
This branch does not contain any changes — check it out on your local machine to do some work.

[Check out in SourceTree]

You can also use this command to check out your branch:
```

Clicking the `[Check out in SourceTree]` button, I get the popup for SourceTree.

I can see the branch initially, but then it disappears before I can do anything.

Locally, I have no commits outstanding and nothing to push/pull.

Initially:
Becomes (after about a second):