After you goto https://www.sync.opera.com/ and reset your passphrase (where it then says you have no data), restart Opera, goto the URL opera://settings/syncSetup and make sure everything you want is set to sync. Then, things will sync to the server using your Opera account credentials where sync.opera.com will then show stuff again. Then, if you want to encrypt your stuff on the server, go back to opera://settings/syncSetup, enable "Encrypt all synchronized data with your own sync passphrase", and set a passphrase.
Another thing you can try is to goto the URL opera://about, take note of the "profile" path, goto opera://settings/syncSetup, set "Do not sync data", goto https://www.sync.opera.com/ again and reset your passphrase if there's data there, click the icon at the right of the address bar for Sync, and click the little logout button, close Opera, and delete the "Sync Data" folder in the profile folder. Then, when you start Opera, you can set up sync like you did the very first time you used it.