Principle Version: 5.7
macOS Version: 10.14.4
Sketch Version: 55.2
Description of what you need help with:
I was working on a principle file and clicked into a symbol - and the file become unresponsive.
Now all my backups are doing the same - when I open the file the screen just goes blank
try restarting your mac and then hold the shift key while clicking on the Principle app icon. That will prevent the file from being reopened on startup and may bypass the problem.