Does this device have the same connection (e.g. through the same Wifi network, cellular network with the same APN, etc. and the same firewall exceptions) as the other 100+ devices?

It is using a similar Cellular connection as many other devices.  We use both AT&T and Verizon but have not yet had a problem with either. 

Samsung ELM license server may be temporarily down for maintenance.  Maybe you can try again a few hours later and see if the problem persists.

Are there other reasons for activation to fail other then connection related?

In the last few years,  connection related problems are the only causes I encountered.

However, I recently heard that Samsung has recently released some new low-cost models with stripped down firmware image (many KNOX related library module not included).  Development of some of the firmware in those models had been outsourced and may not work as smoothly as other internally developed models.  As I have no such devices on hand to test, I am not sure if those device models need or work well with ELM license.  

Thanks for the info.  I'm going to assume it was a connection problem or a temp outage and work with the user some more.  I appreciate all of your time on this!