not to sound too negative, but if you're having so much troubles with this error, its not really efficient. have to say i cannot remember the last time i had this error (outside of the fusion tab) though.
Actually, it's the first time I have run into this problem. I typically record with multiple cameras in 4k, have 80 or so edits in a 10 min video and it renders in 11 or 12 min. I was just shocked that Resolve would take hours to superscale a 1080 web cam video up to 4k when it renders my 4k video so quickly. This is the first 1080 video I've ever tried to upscale so maybe I have something wrong in the settings.