I had the same issue with Motion and it had to do with the preview icons in the browser. Sorry I can’t be specific but maybe change your bin view settings to list.
If the clip name is underlined on both tracks they are linked. Unlink the audio Apple (Command) L. If the clips are stereo they will have the small green arrows pointing at each other. Option L to make stereo pair or not stereo pair. If the clips are not stereo you can Option click them and delete.
Go to you system prefs. and look in the “Other” category. Click on the Flip for Mac icon, click the Upgrade tab and see if you serial number for the upgrade shows up. I had this problem after an OS update.