We’ve run into a few cases of this since a recent macOS update. Cause is unknown, but it has been observed that if you reinstall Scrivener from a fresh download, and also reset its preferences, the problem can go away.
To reinstall Scrivener:
If you have the direct-download version, please close Scrivener then download the latest version from https://scrivener.s3.amazonaws.com/Scrivener.dmg and install that instead, replacing your existing installation.
If you have the Mac App Store version, close Scrivener, then drag the application from the Applications folder to the Trash folder and empty the Trash. Then open the Mac App Store, log in with the same Apple ID as you used when purchasing, and reinstall Scrivener from your Purchases list there.