It happens with a specific page or with any?
Disabling adblocker didn't work, A large chunk of it is youtube, but other pages also give a larger than normal RAM usage. I tried this on my laptop and it doesn't do the same thing. The task manager still shows a large number of of listings from Opera. Installing and booting up a portable version does the same thing even with just speed dial open.
I am using windows 10. Opera version 52.0.2871.40