We are having the same issue with iPhones. Recently upgraded routers in the house, still having same issues with multiple phones. Calls drop at exactly 3 minutes. I think this is a Verizon issue.
Have attempted to call Verizon and cannot get through. Is Verizon working on this?
We know how important it is to have your Wi-Fi Calling working for you. You mentioned, you replaced your router recently. Have you attempted to refresh your connection with a network settings reset?