I have an intermittent problem with Opera Mini on iOS and it's been there at least since Ver. 12. Many pages don't stop loading which leads to funny effects afterwards like reload always being the "stop loading" button and re-loading way too much stuff when going back in the navigation history. This happens both in Opera Turbo and "no compression" mode.
A page that prominently shows it is http://www.ebelholztechnik.de. Go to that page and see the progress bar. It goes to 100%, though a bit slower than other browsers, then after a split second the progress bar appears again and then never finishes unless one hits "stop loading".
This does not happen with Opera Coast, Chrome or Safari on the same device, same OS.
A note: I'm on iOS 9.3 (latest public beta) but I can't imagine that that makes much of a difference. I have deleted and re-installed Opera Mini several times.