Dell Venue 11 Pro LTE Broadband card gone bad

In May 2015 we purchased 15 of these to the tune of over $15k.   So far I have had NINE  (out of the 15!) have the LTE Broadband cards go bad.   They slowly start having issues connecting... sometimes a reboot will fix the issue, then eventually, they just stop working entirely, and don't show up in device manager as being installed. Instead, device manager shows "Unknown USB Device (Device Descriptor Request Failed)" under Universal Serial Bus Controllers with the dreaded exclamation point next to it (screen shot attached).  Thankfully I purchased a 3 year extended warranty through SquareTrade when I got them- which has more than paid for itself @ this point (the cards are $260-REFURBISHED through Dell), but the problem is still a HUGE inconvenience since we have a business to run.   I'm wondering who else has had the problem?

I've contacted Dell directly several times as it's CLEARLY a defect when 9 out of 15 having the same EXACT issue, but they will not do anything about it, citing "they're outside of THEIR one year warranty".