iMovie Deleted Everything in Project (Corruption?)

It looks like the iMovie app lost its link to the library. If your library is on an external drive make sure that the drive didn't get unplugged. I don't know whether your project is corrupted. You can look in the iMovie backups folder to see if you can find your project.

To get to the iMovie Backups folder, follow this file path from the Finder menu:

Go/Home/Library/Containers/com.apple.iMovieApp/Data/Library/Caches/iMovieBackups

When you get there you will see a list of previous backups of your iMovie library.  Click on one dated just before your issue started.  iMovie will open in that library.   Navigate to your projects browser (where your projects are displayed as icons) and see if your projects are intact.

If the above is unsuccessful, try shutting down your computer and then rebooting. See if that restores the link.

If no luck, try booting up in safe mode. (See Finder help for instructions.)

If still no luck, try deleting preferences by opening iMovie while holding down the Option and Command keys and selecting to delete preferences in the box that appears.  iMovie will open in a new library.  Reopen your old library to get back to your projects.  Now see if the issue is resolved. 

If Safe Mode and deleting preferences do not solve it, try redownloading iMovie. To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the trash. Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash and return it to the Applications folder. 

-- Rich

It’s difficult to address this issue without having access to your computer. We could spend a lot of time trying things that may have unintended consequences. You might want to contact Apple Support by clicking on the Get Support item in the upper right hand corner of this forum’s screen. The techs there have the capability of remotely accessing your computer, that we cannot do here. Navigate to a place where you can input your phone number.

Try calling Apple Support. I think that you might find it worthwhile.

To answer your question, the way to revert to your previous iMovie version would be to restore the earlier version via a Time Machine backup. There can be some problems with doing that, so I wouldn’t try it before talking with Apple Support.

— Rich

You are welcome. Best of luck with Apple Support.

-- Rich