This is happening to me too. I thought it was ZVA but I switched back to ZV8 and still lose service with red X. I'm in Queens, NYC. I can't say for sure but I believe it coincided with their PRL update. About couple of weeks ago, for a day, I kept getting the LTE:67 error and since then the signal quality has been bad. I've tried different PRLs but the problem is there.
Also, sometimes the phone shows 4 bars but when I call someone, it changes to one bar or less and takes a while to place the call. I've tried PRL and Profile updates with no luck.