I am fairly upset - this is the exact same issue that I've been having and my local Verizon store has been treating me like I'm a nutter, money grubbing bia who's just trying to cheat them into fresh, new devices.
I bought my Turbo 2 back around Christmas and have since had the device replaced 3 times. When in a call, suddenly it will cut out for the other person, as if the phone was submerged in water or even worse, as if I had trailed off into the distance and then it just went quiet. I have disabled the HD nonsense on all fronts, a feature which I effing PAID for with the purchase of this phone, I have done factory resets, no apps, all of my apps, you name it. No case, new case, different ways of holding it, shaking it, turning speaker phone on, turning it off - it keeps happening and I'm stressed.
Marshmallow just released, so what gives? I am paying full price for this phone. I deserve it to work.