We're currently receiving reports from other users that they're unable to log in each time they launch the QBO app for Mac. Rest assured, our Product Development Team is actively working to have a permanent solution.
As alternative methods, here are the two options you can access your QBO account:
Make sure to update the app to the latest version 4.0.2. You can use this link to download it: Mac App.
In line with this, I'd suggest contacting our Customer Care Team. From there, they can securely gather your company info and add it to the notification list. This is to make sure you're in the loop about its status and the resolution.