My 'Branches' folder has completely collapsed. I cannot show/hide content even though I have over a hundred branches in there. 
 
The Branches section used to show all of my local branches. 
 
If I do a search, then matching branches will display and if you clear the filter the list closes again, but this is nowhere close to a solution much less a workaround.
 
If found that if I right-click on Branches section and create a New Branch, then all of my local branches display.  If I delete the "dummy" branch, the Branches section hides itself again without showing the Hide/Show button.  Again, this is not a solution as it's too obscure of a "fix" and requires a dummy branch sitting around.
 
Here is a reference article with other people experiencing the same issue: https://community.atlassian.com/t5/Sourcetree-questions/SourceTree-sidebar-Branches-folder-no-longer-showing-content/qaq-p/750551