INA296A: Seeing there is a -400mV in the path where am measuring the current

Gils,

Thanks for the question and using the E2E forum.

Due to the U.S. holiday we are not in the office. Someone will reply when we return on Tuesday, 9/2.

Hi gils, maybe i have an idea which you can check in the meantime. I had a quite similar problem the other day with the INA199:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1558902/ina199evm-measuring-led-current

Basically my problem was, that the INA199, aswell as your INA296A are consuming a little current out of the measurement path. Depending on the circuit it can cause a voltage drop, because you are basically creating a "new path" for the current to flow.
INA296A is specified with about 35 uA. If we calculate the theoretical resistance value we will get 400 mV / 0.035 mA = 11.5 kOhm. Maybe try to swap the INA with a resistor in that range and see if the voltage drop is comparable. 

As you can see in my referred post the solution was to measure at a point, where that doesnt effect the circuit or use a device with ultra-low input bias current.

If that doesn't help maybe you can provide a little sketch of your circuit.
BR Nico

Here is the simple sketch for your reference. without any source am seeing -400mV in the measurement path. and when am applying some voltage in to the line am seeing a voltage drop in the line