Half gain measured versus configured on signal

Hi,

We are using the AD7190 in single-ended mode, bipolar, with AINCOM at 2.5V

We have an unexplained ratio of /2 (half) in our results after amplification.

Example of the issue

We have the AD7190 configured bipolar with a gain of 8

Measured voltage at AIN is 2.584V
With a common voltage AINCOM of 2.5V (so 0.084V AIN input voltage after common voltage removal)

Measured voltage by ADC after PGA gain is 2.839V

So very clearly a x4 gain applied on the 84mV input signal. (0.339V = 4 * 0.084)

What are we doing wrong ? Why would our gain be half of what we expect ?

Pins of the AD7190

REFin- = 0V
REFin+ = 5V
AVdd = 5V
Dvdd = 3.3V

AINCOM = 2.5V

We understood REFin+ and REFin- to be the full range of the ADC possible reading range, so that's why we put it at 5V

Here is our register configuration for a gain of 8, bipolar

// FullScale : 0x00553EF0
// Offset : 0x00800000
// GPOCON : 0x00000000
// ID : 0x00000084
// Data : 0x75943D95
// Configuration : 0x0000A013
// Mode : 0x0018A003
// Status : 0x00000095

Thank you for any possible explanation,