@OP. You are not alone. This is happening to me too. This is NEW to PM, never was a thing with others. I am seeing cellular data usage between 12am and 4am every nights since I switched to PM. My wife is also with PM and she is seeing the same thing....
Got the same message about an hour ago. iPhone 14 Pro Max, iOS 17.3.1. 5G plan.Just switched to PM a week ago.Seems Kodoo customers had this same issue as well, about a month ago. Was on the carrier side.