@leocg It doesn't interest me what the reason is. All I need to know from Opera Software AS is that they're working on a solution that will give the same usability in 49 as I had in 48. Opera will lose literally 1000s of users over this as business travellers that frequently go to South East Asia, and China in particular will now have to find another secure browser.
After the clean Guest profile pretty much ruled out internal issues I went to the site's tech support forum and sure enough there was a whole thread of complaints about sessions being terminated on logout.
The problem was finally resolved today.
Opera has so many quirky little problems it's easy to suspect it as the problem causer.
On the positive side, using the pristine profiles in my Windows Guest account is great new tool to help isolate issues with both Opera and Chrome.
Ok, sorted it, a blank profile fixed it as the adblocker is turned off by default. It seems those two sites have been poorly set up and if you block ads you also destroy the complete site structure. So not an Opera problem, but a website developer stuffup, it just happened to occur on two sites I regularly visit on the same day. Maybe both sites use the same backend and they were probably recently updated at the same time.
Yes, it did update to 49.0, and reopened all pages after relaunch.
Why it did download developer 51.0 version at the same time remains unclear to me, but OK, so far so good with this regular version.