There is a sort of bug? that can occur when running through a Pre-Stage enrollment on Mac with Sierra and below. After you connect to Wi-Fi, it may completely skip enrollment. We often have to walk back to the Wi-Fi selection and then forward again in order for the PreStage enrollment window to appear, sometimes more than once. That could be what you saw. There is supposed to be a window that says "XYZ organization is going to manage your Mac" or something similar. You might say, "what's the point of pre-staging if it doesn't work consistently?" I don't disagree.

There was also a glitch where some Macs would be slow on installing the JAMF binary and Self Service, sometimes never completing the enrollment even. For those we would run the QuickAdd package but we'd get a popup saying that the device can be enrolled via DEP and we'd still have to complete that process later, otherwise it drives the end user insane cause its kind of relentless.

I am guessing Pre-Staging will be a little cleaner in High Sierra. Hope this covers what you might be seeing.

It is supposed to just work.
But it is also dependent on network conditions being right, if your behind any kind of security layer you might it is not reaching something at apple or one of their geocaching partners that it needs.
It also uses certificates for security so depending on how your JSS certificates are configured you may need to set this to "not during enrollment".

Are the computers plugged in to Ethernet or are you using Wi-Fi? What settings have you configured to run upon enrollment?

Are you at least getting the screen the "Configuration Available" Screen?