@FelixCold The worst thing is as this is a laptop, its battery drains very fast with such behavior of Opera.

@FelixCold And this is how it looks like over time:
(I'm getting tired of restarting Opera browser every half an hour)

This always happens after a while. Restart helps for some time, then again.

This actual screenshot was made right before the latest upgrade, but I have another PC with the same Opera version and same OS (Win10-64bit) and much more load (3 windows with >1k tabs versus 1 window with ~300 tabs), where nothing alike has ever happened or at least I haven't ever noticed this.

In Opera Task Manager I can see that most CPU using tab continuously varies.
Also frequently, "Utility: Storage Service" uses most of CPU in Opera, but killing it doesn't help (CPU usage remains at 100%) and after a few seconds that service appears again.

Since then I have upgraded to the last Opera version, but nothing has changed.

Any ideas?

P.S. It seems like if allowed to wait without any user action for a long time (several minutes), the CPU usage gets back to normal, but just until I continue to work in browser again (like switching tabs & loading pages).