Much speculation on the interwebs is out there, going back well over a year. My VZW rep offered that it's simply incompatible tech, along with other "older" VZW options like their Caller Name ID (which I had to disable), Ringback Tones, and a few legacy Business options (which we also had to disable). The VZW unit works on the carrier's 1X "layer", switching between 1X and LTE will drop the call - I'm guessing that VZW has disabled/blocked some services that rely on 1X to avoid call drops. The phones connecting to the NE would disable data when a call was initiated - VZW never moved to Enhanced CDMA back in the day, and only a few Android phones were capable of simultaneous 3G data and 1X calls. And, it's not an iOS thing - there's Android users griping about the same thing.
I'm in a fringe area on a job site, and I've found that disabling VoLTE has yielded a more-solid LTE data connection and I'm not missing calls now like when I had VoLTE enabled. No internet yet here, so the old NE is still in the box...
I had an ATTWS line up to a few years ago and had a Microcell - different tech in that box, still hated it. The VZW NE worked well for voice calls. I'm back with ATTWS and now carry one iPhone 6S for each network. I have strong enough of a signal on my ATTWS iP6S that I've enabled VoLTE and HD Voice across carriers is frickin' awesome; I've not been around wifi yet so no feedback on that feature yet...
