This happened to me a few months ago. The gauge took maybe 20 minutes to gradually show that I had a full tank. At first, I thought the tank hadn't been properly filled, but once I realized it was just going slowly, I didn't let it bother me. I'm happy to say that it hasn't happened since.

sometimes after fill up, the gas gauge is slooow to come up the the real amount. Especially slow when the fill up started above 1/2 tank.

Lincoln MKZ is two months old and I filled it up today and it took the entire day for the gauge to reach the full mark.

Sometimes after filling up the car, the gas gauge doesn't update its status for maybe 20-30 minutes. It slowly gets up there, but not right away. So if I go home after filling up and turn the car off, I forget the next morning and I see the car almost empty and then start heading to the station again before I remember.