I've found doing the mask in fusion will work better, and to find the most complicated frame first.
Davinci Resolve
A place to talk about Davinci Resolve and post tutorials.
Really? I tried every which way. Still some flickering and jumping, even with a green screen. I think the AI improved recently, so it might have already been fixed.
There's a lot of variables. I'm curious what codec and bit depth your footage is in.
Another trick is to use it in fusion and use multiple magic masks for different body parts, then multimerge them together and combine with traditional roto. If you did that I would suggest rasterizing out with a saver node so you don't lose your work.
I like that last tip. I finished the project, but I might go back to see if I can work on those couple of scenes. I don't think the audience would notice it unless it's an editor and/or fx person, but that might be wishful thinking.