I finally found something that worked for me I had around 3 cinematic video files that just would not import, tried re-connecting, restarting devices. I then noticed that when connected to my Mac, if I tried playing that video on my iPhone, it showed the "i" icon and said "An unknown error occurred while playing the video." So I duplicated the video, and then re-connected to my Mac and boom! It finished importing within 5sec. Surprisingly now it was able to import both the new and original version, and I was able to hit play on both on my iPhone. Weird glitch, but I'm happy I found a way out