Apple DEP auto enrollment - iOS

Hello!

I have 8 iPads that are setup through Apple DEP. I have Sophos and Apple MDM communicating and can see the devices in Central.

 

However, 4 of them became managed, the other 4 did not. I have had the client factory reset the device, and it still did not re-enroll as managed. I have un-enrolled the devices and also deleted them from Central but they still pop up as unmanaged.

I am just not understanding what I have done differently when the first four and the second four used the same process. They were just a few months behind one and the other.