I've had two Pixels and so has my wife and both phones have data/connection issues. My signal strength is about 10 points weaker when HD voice is enabled as opposed to when I go through My Verizon and disable it from my account. I know others have this issue and I am wondering when Google/Verizon will send an update?
It's a strange issue. It doesn't happen everywhere. A few location around town but my house it one location which sucks.
I just did some experimenting; I've had HD calling OFF (disabled) on my Pixel because of the audio on calls cutting out from time to time. I thought I'd see if there was a difference if HD calling was turned off.
My signal gets worse when HD calling is off - turning it on is a bump from -109dbm or so to -99dbm (neither one is spectacular but most calls here at home connect and stay connected). So I'm seeing the opposite of your results...interesting.
Actually the bump in signal strength only lasted for about 15 minutes then reverted back to what it was previous. I hope Google and Verizon work it out soon. The signal at my house sucks with the Pixel but with my Nexus 5X I have perfect signal.
Adding a post to this. My cellular connection drops constantly with the Pixel I activated two days ago. Highly covered areas, indoors, outdoors, it doesn't matter. It's infuriating. Additional details: New SIM and old SIM from Note 5 have the same issues. Neither one is really better than the other.