I have only tried to save it twice because it's super annoying to do it all over again.
But I tried to save after the love scene, and after trying to beat Marline but losing.
I think this is a browser specific error on your PC. Are you using Chrome? It might be blocking third-party cookies/data so it's preventing you from saving. To find the setting, open Chrome settings, type "third" in the search box, click the Content Settings button, and view the fourth item under Cookies. There should be a "block third party cookies and data" option and you should uncheck that and then restart your browser.