The exact same thing happened to me. I ended up running all the malware suggestions (Malwarebytes, HitMan, AdwCleaner, JRT, and nothing was found. I ended up backing up my profile info to another folder, uninstalling Opera and rerunning all the mentioned programs, ran Ccleaner as well, rebooted, then reinstalled Opera. Everything's working fine now (fingers crossed, knock on wood, etc.). It was extremely annoying. I feel your pain! Dealt with it for ten days on vacation, which made me switch to Chrome for that period, but once I got home and was able to properly research and print the info I needed, the problem seems to be resolved. I'm adding my speed dial items and so far everything is functioning normally. My issues also started after the upgrade to 31. I do have 31 installed now, and after the wipe and reinstallation, the problems do seem to be gone. I had AdBlock Pro installed, too, but it didn't help with the popups.
This is the site I used to eliminate the tech-support popups I was getting. Don't know if you're getting those but it was helpful anyway. Good luck!