Random Clips Disappear in Timeline Upon Opening Project Weeks Later

Upon opening multiple projects weeks or even months after finishing them, random clips are gone from the timeline. FCPX does not have any errors or warnings saying clips are missing and the clips are still present and working in my library. The pic I attached shows all the black/blank spaces where clips should be. No clips have been moved or deleted from my computer or hard drives. I thank you in advance for any thoughts/resolutions and please forgive me if this is posted in the wrong place. I signed up because of this issue and am new here. Thank you! 

I'd go to your Movies folder, to the Final Cut Backups folder, and try opening some of the most recent backups.