Just to emphasize Dave's last comment, here's my experience.
If you have missing media in your timeline just return it to the appropriate subfolder (i.e., OneDrive, Dropbox, iCloud Drive, etc.) in the LumaFusion UserMedia folder and it will automatically relink to the timeline without loss of any edits (e.g., Color & Effects, Size, Keyframes, etc). You might have to shut LumaFusion down and reopen to see the relinks.
I to some how either I clicked on something or a glitch happened but all my files got unlinked. Now, maybe somehow one fill got deleted but I can not see how all my files got deleted or moved. I see all my Files in my Photos folder/app. I am going to have to see if I can manually like them again but this is a pain and a lot of time wasted. Double clicking on the area where the video clip should be did not do anything. Also it looks like even my titles became unlinked. I will upload a screen shot.