I have had that same frustration with videos showing the yellow media pending on older projects. I've tried all the fixes - Enable, Disable, Copy, make a new project (not really viable for the big project I'm working on!) etc etc.
When I did the copy video thing and I could see it in the project while the original was black with just audio. It occurred to me that a new XMP file was created with the copy in the folder the clip lived. So..... I deleted the XMP file for the original clip in the folder..... and hey presto! ....the clip gave me the loading blue bar at the bottom and "popped" back up in the project with a new XMP file.
If you are frustrated with all the workarounds and nothing is working, try deleting all the associated XMP files in the folder where the original videos are (my XMP files were at least 2 years old) and see if that fixes the problem. You will get new XMP files created for the project so if you have lots of clips like I do, it may take a bit of time. Saved me having to redo 4 sequences of 30 minutes each with at least 7 clips in each sequence!
Editing, Error or problem, Freeze or hang, Import, Performance