Windows 7 Home Premium (x64) + Opera 67.0.3575.53
For some time, when I start Opera browser, I get the error "Your preferences files cannot be read. Some features may be unavailable and changes to settings won't be saved". Any such error results in logging out of all websites to which I have been logged. Including Opera account. Sometimes logins and passwords are remembered and all I have to do is press "Log in". Sometimes, however, I have to enter them again. Restarting Windows does not help. Uninstalling the browser using Revo Uninstaller also does not help.
IMPORTANT: The same error occurs in both the installed version and the portable version.