It's not the source of the video, but I did have a slight breakthrough. They messed up the blur on ine of their videos, which revealed a watermark from the streaming site they use to find movies. A quick google search revealed this site:
https://www.iq.com/movie?lang=en_us
It's a mainstream Chinese site for streaming Asian movies. Whoever is running that YouTube channel is just (badly) ripping videos from there, and reposting them on YouTube. It still sucks trying to pinpoint the source of each of their videos, but having the site they're pulling from may make things slightly easier.