I have one, it's worked for me with one of my two VZW iPSM, my main driver to this point (on B5 now, but that didn't really matter as I took one additional step with B2). My second iPSM is still on the 12.0.1 FW, partly for comparison...
I'm also not convinced that it's a iPhone XS/XS Max thing, or an iOS thing. I have a few employees on ATTWS Kyocera LTE flips, and my mother is also using one while out on the road for a month or so - they use a variant of Android. I use an Android-based ATTWS MHS as well. They're all experiencing dropped calls, No Service issues, going straight to VM. I also have - and have tried - VZW iPhone 6 handsets, used as backups when my employees drop their iPhones in a creek or a river, an occupational hazard - this have worked without issue for years, and two of them are still on 10.3.3 and are also experiencing connection issues, and have for weeks now. Calls to landlines in some geographical areas are also not connecting or not working as expected, also going back at least 3 weeks or so - regardless of network, carrier, or landline operator.
That written, the "extra" step that I took is calling VZW tech support and asking them to re-provision my main line. It's worked pretty well so far, and it's not the same as clearing/pushing carrier updates. I periodically have to stay in a "roaming" region for several days at a time (on USCC, in rural areas), and I have to have VZW tech support re-provision my handset.
Be in a non-Extended network area, connect to wifi, call in on different phone line, ask for a Level 2 tech, ask to have the line re-provisioned. I carry an iPad Air 2 or Pro (both VZW LTE) - the re-provisioning option is built into the OS, and it works perfectly, and I don't know why it's not available in the iPhone OS...