Hello Chad,
Sorry your having issues here. First, I would like to point you to errata ADC29 for this chip. It seems the calibrations points for any reference voltage @ 30C cannot be trusted on some devices. One key difference between a good calibration and a bad one is a 30LSB difference. The only work around for this errata is to calibrate at 30C on the application level.
now this errata does state the values at 85C should be valid. From what you are describing, something similar may be happening here. I would suggest as a workaround to calibrate the Bad units at 85C via your application. Some internal investigation on our side to determine the cause of this.
Regards,
JH