I just got off of a 2 hour tech support phone call with AT&T that got escalated twice. Apparently the problem is supposedly with my SIM card that I have already had swapped twice and not the phone. So if you look at the SKU number on the actual SIM card, not on the larger credit card that you pulled it from, you will see a 5 digit number followed by a letter G or a letter O. So the G cards are the problem and they cause your data plan to push out as a 4G (NON-LTE) plan which eventually leads to the problem we are all having that can only be band aided by adding secondary APN information or hard resetting your phone.
Another thing I learned, apparently your phone is supposed to have blank APN information listed in the settings. The add APN button under cellular settings is to add a secondary cell network. Your primary APN is hidden and created by your SIM card. I was instructed to go to my AT&T store tomorrow morning where they would supply me with the correct LTE SIM card.
I will update here after my trip to let you all know if my problems are fixed.