I am unable to reproduce this issue on my test site. With the latest versions of JFBConnect 7.1.1 and CB 2.0.15+build.2016.12.02.00.46.33.ef62bd55e, I created a required Terms and Conditions field. It shows properly on my JFBConnect login / register view and the registration doesn't proceed until it is checked, as expected.
Could you provide backend access to
berlin.international-friends.net/ so that I can see how the fields in CB and the JFBConnect > Profiles > CB area is configured to see what's different from your site versus mine?
-Melissa