sometimes the ac unit is working so hard because of heat you may want to check out side to see if there is frost around line, the fins all around are clean and clear of leaves or other air blocking material. Also sometimes the unit in the house above the furnace that connects to ducts can freeze up because it gets dirty over several years. if you see any water by floor where unit is then that would be the case. some places to start
Me too same issue! Had my NEST 3rd gen thermostat for over 3 years. Earlier this summer I enabled Learn Mode - inside temp was between 72 to as high as 78 degrees. With the externally high Arizona temperature I disabled Learn Mode, but the unit acted as if Learn was still on.