I have a similar problem too as I’m trying to upload .mp4 file but it can’t find the pathway to the file. Initially it worked with my 4.27 and I could upload the video and posted on plane and everything went well until I forced deleted the video to change to different video and then the nightmare started.
As I don’t use C++ for my project, please advise what should I do. My project is created by using 4.27 assets so I can’t go to a version below which is the media source still working. I tried to uninstall and reinstall 4.27 and still doesn’t work.