Same problem. Makes https://yandex.ru/maps/ and https://www.google.com/maps/ completely unusable. https://soundcloud.com/ has this problem too but it's less intense.

Problem seems to be connected to loading new data, and while it happens opera's task manager goes insane with tasks flickering all over the place. Flickering stops when everything is loaded, but comes back when new information needs to be loaded i.e. new map region or new song.

Bug only appeared in newest version. Never had this problem before.

Edit: hardware acceleration was off. enabling it fixed the problem

Bug continues to exist. No VPN, no firewall, no anti-virus on my end, and this is how task manager looks like after about an hour of watching a stream. Eventually, after filling up all available memory tab will crash.

http://i.imgur.com/HH364Jp.jpg

I've posted my specs before in this thread.

I don't use any VPN, no firewall or anti-virus, usually only two things that are constantly running when I'm using Opera are Discord and Logitech software for my headphones.

I've decided to test different livestreaming services and see what will happen. I've ran opera in private mode, opened one stream at a time and let it run for 5 minutes.

Here are my results. http://i.imgur.com/Gq5aplv.jpg

Then I've opened the same streams in Chromium. Same quality, same amount of time, vastly different memory consumption. http://i.imgur.com/hQZDlzf.jpg

My specs:
CPU - AMD FX 6300
Video - Geforce GTX 750 with 375.70 drivers installed
RAM - 8 gigs
Windows 7 x64 pro
Opera 42.0.2393.94
Chromium 57.0.2964.0

Can confirm memory leak. Happens both on youtube and twitch, haven't tested any other livestreaming sites yet.

I've opened a stream in incognito mode and left it open while I was registering here. Here are three screenshots of my task manager. First picture taken right after I've opened a stream, second one about 5 minutes later and next one 10 or 15 minutes later. As I writing this post, it's already at 1 gigabyte.

http://i.imgur.com/fqmrpNX.jpg