Things that come to my mind: 1, you shouldn't need pepperflashplugin-nonfree, and 2, can you disable NoFlash and see if you still have problems? If NoFlash is complaining, this seems more a bug on their side, rather than Opera's.
I can not load some games I like to play on facebook because of Opera and Flash player. I just get a blank purple screen when trying to load Hit It Rich Casino Slot game on Facebook using Opera. I used to like Opera and it worked fine up until a month ago. Now I am back to using Chrome because it is the only way I can play the game.
They are about issues with Flash that came with the changes in Chromium that now requires white-listing of pages for Flash to play on them while this topic is about an old problem with Flash playing on Opera for Linux.