This was the hot thread back when I spent hours on the phone with Tier 2 to be told different answers for pretty much every call about similar issues with my S9. It was finally boiled down to let's replace your device. I now see that this is supposedly an I device only issue but definitely have similar issues with a samsung in that anywhere from 5m to an hour after connecting to wifi with wifi calling on both calling and texting will stop working completely. Ironically my wife's iphone has no issues with wifi calling and dropped calls. I opted not to further pursue warranty replacement as I don't see how it can be a hardware defect if it works for some amount of time after connecting to wifi but then just stops working. Also from way up thread to some extent the prefer cellular is a verizon network thing and can affect verizon phones as well in areas of barely having service and trying to use wifi calling. I have dealt with multiple situations where wifi calling doesnt fix the barely gets service or sometimes gets service locations without using the VZW microcell. Also for those interested it did appear that while I was at one of these locations (family) my phone and the vzw microcell were more than happy to play nice together giving me service.
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