After attention was called to the uneven trending in the temperature of Zone 2A, I checked the heating coil and found that while the automation system was calling for 100% heating, the unit was not heating at all. I found that one of the 40 amp line voltage fuses had blown. This fuse also supplies line voltage to the control transformer which powers the control board, meaning the entire duct heater was down. Further troubleshooting is needed to find the cause of the blown 40 amp fuse, which will likely involve replacing heating elements.