The problems are very clear as you increase speed you need more towers and no towers where added in my area for 4G
also AT&T has internet powered phone boosters known as Micro Cells they act like miniature cell towers you hook to internet to provide coverage in spotty areas and they are playing havoc with cell communicators.
I have spent many days just going around installing boosting antennas and moving and relocating units to try and get coverage to end up having to switch to Verizon CDMA I am done with AT&T and I am not the only one I hear nothing but complaints from friends and customers who have AT&T phone I have a At&t pay as you go phone use to get perfect signal at my home and now poor signal and tower is 1 mile from my home. I am done with you AT&T you rolled out that new service knowing you could not support it and you want to go to 5G which will make things even worse .