Premiere Pro missing video footage

Hi, I faced a really weird problem while working on Premiere Pro with Macbook Air: I had made a project in Premiere Pro where I uploaded my footage from Photos like usually. After editing and saving my project, when I opened that project later again, Premiere claimed that all the media was "missing", although all the files were in the same place, in Photos folder just like before. I haven't changed or deleted any of the files that I used in the project, and I can't locate all of them again, because those aren't really missing. 

What should I do?