I have been using the gateway quiz so that students can do two graded submissions (or attempts) on one version (see quiz settings in screen shot below).
We have done some testing and found that if the first attempt is not submitted before the grace period expires, the students do not get a recorded grade (as expected). However, if the students submit their first attempt before the grace period expires, the grace period becomes infinite for their second attempt. In fact, we found that a submission may occur (and the grade will be recorded) after the quiz due date.
If someone could help with this, we would really appreciate it. We are hoping to fix this as soon as possible.