@donq
I also experienced the same issue. I disabled every extension including opera built-in ads block. I also experienced this on Opera on 2 platform windows and linux, both were latest version.
Chrome browser did not have this problem.
When I open dev tools to check for errors, I have this:

Refused to load the script 'https://payments.google.com/payments/v4/js/integrator.js?ss=m2' because it violates the following Content Security Policy directive: "script-src 'unsafe-inline' 'self' 'unsafe-eval' https://apis.google.com https://ssl.gstatic.com https://www.google.com https://www.gstatic.com https://www.google-analytics.com https://www.googleapis.com/appsmarket/v2/installedApps/". Note that 'script-src-elem' was not explicitly set, so 'script-src' is used as a fallback.

m=_b,_tp:391 WARNING!
m=_b,_tp:391 Using this console may allow attackers to impersonate you and steal your information using an attack called Self-XSS.Do not enter or paste code that you do not understand.

Hope this helps,
Regards !

Today I upgrade to Opera 54 and still have this problem (with HW acceleration off). Finger crossed on Opera 55 maybe.

@nvmjustagirl I have captured the crash log in this paste:
https://pastebin.com/LeBjsezN
My laptop is Lenovo Y50 with UHD touch screen, intel i7 4710. I have never had a problem with video driver with any apps before. Just this Opera seemed to crash once in a while.

The message seemed to indicate:
Trying to call glGetShaderPrecisionFormat without current GL context
Trying to call glClientWaitSync without current GL context
Trying to call glGetError without current GL context
GpuProcessHostUIShim: The GPU process crashed!

This has happened randomly, and not on a particular website, eg: this crash log was captured when I was checking gmail.

@nvmjustagirl I have disabled all extensions and confirmed blackouts still happened. I have Opera 53.0.2907.99 running on windows 10 EDU x64 build 17134. Graphics 1 Intel HD 4600 driver ver 10.18.15.4279, Graphics 2 Nvidia GTX 960M driver ver 24.21.13.9731. I don't think the Nvidia graphics was running while I was using Opera. If it was I would have noticed activity in the tray bar.

Would like to report that with Hardware Acceleration enabled, Opera rendering engine seems to crash once in a while, when it does, the whole screen blacks out for a split second then comes back normal. But this is still manageable, just a minor annoyance.

@nvmjustagirl Thank you so much for the suggestions ! Did not try the Compatibility setting but I went to Settings and saw the Hardware Acceleration unchecked so I checked it and restarted Opera. Now for practical purpose the issue no longer exists (although still can't compare with with the responsiveness and smoothness when scrolling on a 1080p display monitor).
Finally after so many revisions I have this problem fixed thank to you!

As far back as Opera 40 I have noticed this issue. It is getting worse as more websites are getting affected. The issue is when I use Opera with my laptop screen (UHD 4k display), all of Opera built-in feature pages (Settings, Extensions, History, News feed ...) are freezing and laggy. If a click a button/scroll on those pages, it takes 5 seconds for that click to register and the CPU revs up all the time. I have to close all of the pages for Opera to return to normal.

Recently I noticed websites can be affected as well, some of examples I list here are from ebays. If I navigate to these websites, scroll to the middle of the page that's when the problem starts. Again, I have to close the page for Opera to return to normal. Say middle click on the tab, 5 seconds later the tab is closed.

https://www.ebay.com/itm/LED-Display-Module-Delay-Timer-Relay-Control-Programmable-Switch-Car-Buzzer-12V/272301547347?epid=508943557&hash=item3f666fdf53:g:SKAAAOSwEjFXf2sg

https://www.ebay.com/itm/12V-DC-Delay-Relay-Delay-Turn-on-Delay-Turn-off-Switch-Module-with-Timer/172524324192?hash=item282b404560:g:5v0AAOSwWxNYnSjB

The reason I firmly believe this is DPI scaling issue is this problem only happens when I use Opera with High DPI screen. If that same laptop, I plug to an external 1080p monitor then none of this issue happen. Opera is smooth and responsive like it should be. By the way, Chrome browser does not have this issue why Opera ?

I have submitted a bug report with this number: DNAWIZ-29908. Please let me know what I can do to assist your testing.

I cannot access the Extension page, settings page because they are so laggy and unresponsive (Opera 47). I believe it has to do with my laptop screen is high resolution as I do not see this problem with my work computer.

Since the recent Opera update, I am not able to change any Opera settings or Extension settings since those pages are slowed to a crawl.

Mine was the internal settings pages like Download page and History page and Settings page were very laggy. I thought they were going to crash but they were just slow. Also, my CPU revved up when I went to those pages. Definitely there were some bugs, no doubt. Normal web browsing appeared to be normal. Speed dial was quick to open and smooth.