Who I have the same questioned this topic

You may not be getting answers because their may not be many of us experiencing this. I have not had this issue on either of the iPhones in my house so I really can't offer anything but speculation. The usual suggestions are reset network settings, make sure your SIM card isn't bad...rule out a service issue in your area by seeing if any other Verizon users in your area are having the same issues...restart/reset/restore your device...troubleshoot with Verizon and/or Apple. But if none of those have helped you out I'm not sure what could be going on. If you have an Apple Store in your area you can take it to them so they can see the issue occur...they may do a warranty replacement to see if that helps (but if it's not the device and is a network issue then it won't work). I know saying none of this is helpful if you've tried all of it and still have the issue...it could be an issue that is tied to the latest iOS update (I updated and didn't have the issue occur so I imagine it's not a universal bug) then the only fix may be to wait for the next update (iOS 9.3 should be coming soon according to Apple's website but it doesn't specify when "soon" is).