We have a product that use AD7864AS-2 configured to operate with the internal 2.5V reference. When the AD7864 is heated about 65ºC~70ºC (external temperature) and the signal in channel 1 drops below ~0,2V, internal reference voltage (measured on Vref pin) drops to 0V crashing the operation of the AD. If the signal in channel 1 keeps above ~0.2V, even with high temperatures, AD operate without problems. If the signal on channel 1 turns above 0.5V after the crash, the system returns to work.
The "Fig 1.jpg" shows the schematic of AD on our board. We already have a 0.1uF capacitor betwen Vref and AGND.