We run into trouble with AD8422ARMZ, the input bias current is 700 times to large.
The circuit is attached, Vref is 2.5 V, we get 7 mV voltage drop at R302
Only newer datecodes (517, 535, 608) affected, datecode 424 works as expected. Direct replacement of newer datecode with an 424 result in an voltage drop at R302 under 0.1 mV.
The check with your "Instrumentation Amplifier Diamond Plot Tool" shows all in range.
What was changed ?
Thank you for the support.