At the URL opera://settings/content/siteData, make sure the default behavior is set to "Allow sites to save data on your device" and make sure all customized behaivor lists are empty.

At the URL opera://settings/cookies, make sure it's set to "Block third-party cookies in Incognito mode" and make sure the allow list is empty.

While Opera is closed, in Windows Explorer (File Explorer), in both "C:\Users\yourusername\AppData\Roaming" and "C:\Users\yourusername\AppData\Local", right-click on the "Opera Software" folder, goto "properties" and click the read only box so that it's clear (all white) and click "apply". Then, switch to the "Security" tab, make sure your username is there and make sure it has full control (all permissions set to "allow" except "special permissions") and click apply if needed. Then, OK out.

Then, in Opera, goto the URL opera://settings/clearBrowserData, switch to "advanced", set the time range to "all time" and check just "cookies and other site data" and clear the data. This will log you out of all sites.

Then, close Opera and delete the "Cookies" file in "C:\Users\yourusername\AppData\Roaming\Opera Software\Opera GX Stable\Network".

Then, make sure the time, date, time zone and daylight savings settings in Windows are correct.

Also, make sure you don't have any programs like CCleaner clearing Opera's data.

Then, start Opera and log back into your sites and you should be good to go.

Also, always make sure you close Opera yourself before you shut down or restart Windows. Never leave it open where Windows force-shuts Opera down.

If you still have issues, it could be caused by Opera Sync and syncing settings.