Regarding Flash player issues, make sure you have latest ppapi flash plugin installed.
For those who may be uncertain about this, like me, here's what I did.
(1) Go to opera://plugins and search for "flash" to see whether it's present, up-to-date, and enabled. As of today (9 November 2015), the current Flash version is 19.0.0.226.
(2) If not, go to http://get.adobe.com/flashplayer/otherversions/, select your operating system in Step 1, and in Step 2 select "FP 19 for Opera and Chromium - PPAPI".
(3) Follow the installation instructions (be careful to uncheck the sneaky little box that will try to install Chrome as your default browser!).
(4) Restart Opera. Perform (1) again to be sure Flash is there.