If your app looks like this when you open it then please continue reading for a fix.
To fix this problem start by downloading a fresh sidebar configuration file.
Stock +: (download link)
Stock + Pro: (download link)
Find the downloaded file and double click it to unzip the archive. (.zip -> .spdata)
With the file downloaded and unzipped, go to the app's File menu > Import.
Select the new .spdata file in the Open dialog.
Click on Open. A dialog will appear asking if you want to overwrite your existing sidebar data. Click on overwrite.
The app should be working now.