I've got a Chauvin Arnoux C.A 5220 DMM that bottoms out at 9 mV.
Even with the inputs shorted and in "Velec" mode (270 k input
impedance), it never goes below 9 mV.

The problem is only for AC. In DC mode, it *does* go down to 0.

Any idea what could be the problem ?

It's built around a JRC NJU9210BFC.

--
André Majorel URL:http://www.teaser.fr/~amajorel/
"Je regrette le Concorde. Au moins il vous amenait directement à
l'hôtel." -- Cyrano