In general when you receive a 404 error for a callback on social network login, this is because the application's redirection URL's have not been set up correctly. Please visit our application setup guides for the social network you're seeing the error on to verify that they are set up correctly -
www.sourcecoast.com/jfbconnect/docs/soci...etwork-applications/ If this doesn't resolve the issue, please provide more information such as which social network you're logging into and a URL that the error is occurring on.
Also, this statement is very vague - "from nothing to login via social networks started to not work", so if there is something other than social network login that is also not working with JFBConnect or SCLogin, you will need to provide more details such as the steps you are taking on the site on which specific URL's, what you're expecting to see, any error messages that are displayed, etc.
-Melissa