Over the last week i've plugged the devices in for an hour or more to see if either would connect. It's been about a week since I began trying to connect these in earnest, but it wasn't until today when they both connected. Both were running the debug firmware from @rickkas7.
Upon this success I unboxed a 3rd e-series and attempted to connect. It failed for about 10 minutes before I flashed the debugging firmware down over DFU mode. This time it connected after about 5 minutes (logs available). I reset and attempted again. This time it connected in about 20 seconds.
I'm not sure what the root cause was, but time seems to have healed all of the wounds so far.
I'm going to flash all the e-series devices OTA a few times to ensure I get some data-movement registered with the Telephony partner and hopefully this will keep the devices alive.