The Ext Ref voltage reading from the ADC is 4.20 (0x326c), on another board the data is 4.11V (0x314f), while on a 3rd board it varies from 4.07V (0x30e6) to 4.08V (0x30e8). In all cases the the voltage measured across VREFP and VREFN is precisely 4.096V.
Since the external channel readings are off even more, we suspect an error with the design that could be causing the internal and external readings to be faulty:
Reading back the config registers, they are all the default power-on values except for: CONFIG0 and CONFIG1 which we've set to 0x12 and 0x03. En/disabling the BYPASS (CONFIG0.4) also affects the readings greatly.
What could be causing this issue?