Well, I'm kinda having the same problem. But a little bit different.
For me the memory usage increased with Opera which added WhatsApp and Facebook Messenger into the browser.
It's not a biggie for me, I can live with it (I disabled/unchecked both anyway).
What bothers me is that with Opera 46.0.2597.32 (Windows 10 64-bit) Mixcloud doesn't work fine anymore ... mouse cursor with blue wheels starts to blink after is press "play" button. It doesn't matter do I have just 1 or lots of tabs opened, it keeps blinking even when the browser is minimized or is in the background or other tab is opened. After closing Opera, the blinking stops.
Opera task manager shows same time flashing GPU process ... see gif image below
Same issue also with Google Maps
Sometimes it happens also with Soundcloud and IG, but only when lots of tabs opened and only when scrolling the page. Blinking stops after mouse click.
Twitter, FB and YT working fine.
With Vivaldi, Firefox, Edge no problems with Mixcloud showing up.
I tried without extensions, cleared history, cleaned profile folder, updated Flash player ... nothing helped.
Finally after hardware acceleration is enabled the problem with blinking mouse cursor seems to be gone.
But something tells me it ain't the right solution.
PS! Opera 46.0.2597.32 loads speed-dials a lot longer/slower than before.