Confirm that you are opening iMovie in the correct library (it happens). At the top of the Projects browser screen there is a selection box. Click on it and a drop down display will show what library you are in. Click on the correct library and the projects should appear.
If still no luck, go to your Movies folder (Go/Home/Movies) and control click on your library's icon. From the pop up menu, select Show Package Contents and confirm that your projects and events are in there. Since the library shows 84 GB the projects should be there. You can open the projects and see the contents of the subfolders, but you can't play the projects there because they contain only data and codes. Do not modify, move or delete anything in the Show Package Contents folder or you risk corrupting your library.
If the projects are contained in the library, then iMovie is not linking to them or possibly the library is corrupt. Try deleting preferences to see if that cures it. To delete preferences, open iMovie while holding down the Option and Command keys and select 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. Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.
If the projects are not in there, look in the iMovie backups folder to see if there is a previous backup of the library where your projects will appear. 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.
Failing that, try re-downloading 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. (NOTE: For El Capitan and older, click on the Purchases
tab at the top of the app store screen and then sign in. Click on Purchases again to reveal your purchases.) 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 (if you moved it there) and return it to the Applications folder.
Another way would be to go to your Time Machine backup, if you have one, and restore the library to a previous date. You should restore it to a different location so as not to overwrite the current library.
I can't think of anything else that would explain why iMovie is not reading your library's projects, other than perhaps updating your software to the most current versions.
-- Rich
