Same thing happens to me, Except my situation is a little different. My phone picks up signal where it usually does, but I have noticed here in the past week that when I go to my aunts house (she has really bad service no matter what network you use) my iPhone 11 will not pick service back up itself when I go back into town where it usually gets service fine. I then have to force restart my phone and it has always worked. It’s kind of annoying that my phone doesn’t seem to have the capability of picking service back up when it is lost, but I’m sure they will address the bug in the next update... hopefully.