I was having the same problem on opera 26.0.1656.32 I read the comment about disabling the extensions...went and disabled all four that i had active, and hey presto, the tabs loaded. while i was in the settings page, i also deselected 'Use hardware acceleration when available' under 'system' at the bottom of the page. this last action didn't seem to change anything though. so try and disable all your extensions and see if that helps.
i'm really sad that we're having all these issues. i have been using opera for more than 11 years now, and really miss the old functionality of opera 12 and before. please, please, please, sort out these issues. i have really enjoyed using opera in the past, most of all sessions, what a miss that is. please stay on your own path, as like before. you were so innovative; i just wonder why you couldn't make the chromium version function the same way as the previous. what's that old saying?...if it's not broken, don't try to fix it!