Hey, same here! For better or worse, I use Opera Mini for much of my mobile browsing, and it fares far worse than Firefox with uBlock Origin and ResistFingerprinting. I complained about this roughly a year ago on a similar HN thread, on which a Cloudflare rep also participated. Since then something changed, but both sides being black boxes, I can't tell if Cloudflare is wising up or Mini has stepped up. I still get the same challenge pages, but Mini gets through them automatically now, more often than not.
But not always. My most recent stumbling block is https://www.napaonline.com. Guess I'm buying oxygen sensors somewhere else.