I work in downtown Kansas City, Missouri and my 4G signal has been limited or non-existent the past two weeks with my Galaxy S8. I can barely maintain a 1X connection inside the building I work in even though I had acceptable signal weeks ago. Restarting the phone does help but only temporarily; after minutes, it will degrade back to 1X unless I am literally right against a window. The zipcode for this location is 64105.
Thus far I have not seen even a hint of the 4G service falling back to 3G; it is either 4G (seldomly), 1X (most of the time), or nothing at all (very rare).