I'm having the exact same problem that started 5/25. Opera 45.0.2552.881 (PGO). Windows 10 Pro 64. I don't have Turbo on and I am not using VPN. Extensions: Adblock Plus, Always Smile, Disable HTML5 Autoplay, Download Chrome Extension, Images ON/OFF, PasteItEverywhere, Search the current site.
I've turned off the Adblock Plus, HTML5 Autoplay, and Images ON/OFF, but it doesn't affect what is happening. As others reported, on 5/25, the problem was intermittant. Today, 5/26, it is steady. Google always loads with what looks to be an old version. This is not happening in Chrome and Internet Explorer.
Looking at the page source for the same google search page in Chrome, I see it starts with this:
<!doctype html><html itemscope="" itemtype="http://schema.org/SearchResultsPage" lang="en"><head><meta content="/images/branding/googleg/1x/googleg_standard_color_128dp.png" itemprop="image">
In Opera, it starts with this:
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
I've just tried the useragent switch extension others have recommended. It solves the problem. Of course, I shouldn't have to do that, so there is still a problem either with Opera or Google.