I'm honestly not sure. JFBConnect v6.3.0 is more than a year old and hasn't been tested with newer versions of Joomla at all.
Regardless of version, can you let me know if the same issue happens with standard Joomla credentials or when using the normal Joomla Login Module, mod_login? If so, then I don't think the issue related to JFBConnect at all and may be an issue with the Amcharts extension itself.
I hope that helps investigate things for you.
Thanks,
Alex