I have seen that before especially when the Apple APNS are being slammed at the beginning of the school year. I would check to make sure you do in fact have your ports open so the traffic for the sends and receives to the APNS is not being blocked or dropped with firewalls. Here is the list of ports that the JAMF software uses for everything. HERE.

Firewall doesn't seem to be blocking anything, or at least I'm not seeing anything obvious. Could it be something in the setup of JSS?
I'm trying to think here, if I can see the iPad in the pre-enrollment stage obviously JAMF is talking with DEP just fine. When I go to inventory I'm not seeing anything. So there's a disconnect somewhere...

I had this exact same issue occur back. We had to regenerate the certificate for the Apache Tomcat.

Went into Settings -> Apache Tomcat Settings -> Edit -> Change the SSL certificate used for https -> Generate a certificate.

After that, I was able to power off the ipad and run thru the setup.

I agree check the ssl cert. Also make sure the iPad has the correct date. We had one that was way off on the initial setup and we couldn't get it to enroll until we reinstalled iOS. After that it was fine.

Thank you so much! Updating Tomcat cert worked like a charm. I was pulling teeth trying to figure out the simple thing I was missing.