Hi Christian
I am glad you are able to get it working. Do you have the HPF enabled in the V1 channel? Try enabling it to see if the offset goes away. Anyways, you can compensate for the intrinsic offset in IRMS register value using the IRMSOS register (offset compensation in page 25 of RevC datasheet). To reduce the ripple( fluctuation) in the measurement, try doing an average of multiple measurements as I suggested in my previous reply.
Regards
hmani