I recently upgraded my S8 to Android Pie. Since then, when I am on Wifi, the 4G icon is lit up. In the past, when I was on wifi, it was greyed out. When I use device maintenance to close all background apps, it goes off temporarily, but comes back on in a few seconds to a few minutes. I tried closing individual background apps and have concluded that Verizon Messages +, my texting app, is what is causing this. In fact, when I open the app and close it, the 4G immediately goes off temporarily.
I don't know if this is a problem or if Verizon even knows about it. Is it using data while I am on wifi? Does anyone else have the same issue?