I used to have this issue on other sites but never supjav. Since a long time ago, I upgraded to the pro version for a small annual fee, you get quicker download and auto-save when done. Auto-save is important because sometimes the downloading page can become blank after some a period of time, and if you don't save it in time, you lose all progress. It's recommended not to have too many downloads (more than 5) with cococut at same time, as it can drag on for too long (more than 8 hours) and become blank page.
I usually download 720p version as I don't see a difference with 1080p.