Footage displaying a blank screen in Timeline - Solutions?

I had a large video project handed off to me, and it's a long video with lots of assets and footage that I'm attempting to edit. I had to relink a lot of assets when the file first opened, due to the file project being moved and some links being broken.

The end result is that some of the video footage shows up in the timeline as shown with lines through it and the preview is blank where it is. I don't know what's causing this issue, and I've confirmed the video files I relinked are usable.