I just get an error - but maybe only my profile?

https://invisioncommunity.com/settings/login/?service=2

Your Facebook authorization has expired. Sign in again to resume syncing your profile information.

When I click Sign in I get function not available

Have you considered going to your account settings page and disable the Facebook connection and then enable again. 

Facebook is constantly changing things on their end and it's possible the stored connection details are problematic and you are getting the error message in response to that.  It's also possible IPS might have to make changes on their side to reset their connection with Facebook.