Cookie settings are at the URL opera://settings/content/siteData. The option should be set to "Allow sites to save data on your device" and the "customized behaviors" lists should be empty.
The third-party cookie settings are at the URL opera://settings/cookies. It should be set to "Block third-party cookies in Incognito mode" and the "allow" list should be empty.
You can also goto the URL opera://settings/clearBrowserData, switch to "advanced" and clear "cached images and files" and "cookies and other site data" for all time. Then, you can goto the URL opera://about, take note of the "profile" path, close Opera and delete the "Cookies" file in the "Network" folder in the profile folder and delete the "Local Storage" folder in the profile folder. That will log you out of all sites and clear their local storage, but it might fix things.
Also, make sure the time, date, time zone and daylight savings settings on Windows are correct.