Does VoLTE and VoWiFi work? Your issue can be caused by lack of support for IMS services if an app needs this to communicate SMS. I have seen similar issues on a S9 without IMS support due to Samsung proprietary IMS that can’t be ported to LOS. I have the same issue in my XZ3, no IMS so defaults to 2G or 3G bands that are spotty and will soon be turned off, big problem I hope get fixed.