For me it seems to be happening too. Also when I opened Opera (49.0.2725.47) for the first time today it would freeze for a few seconds followed by the window going '(Not responding)' and this too with just two tabs open. I restarted the computer and it seem better for the freezes but I think it uses more CPU% and Memory than it did before. Also Opera Neon is using less memory (like 900MB) than standard Opera browser for the same tabs.
Opera for Windows