A coarse correction of input offset must be done for the input amplifiers first.
At first sight, the offset voltages in your measurement seem to be slightly outside specification, which can mean that you have either a defective chip or wiring fault in your circuit. I would try nevertheless to minimize the Vrms reading with shorted input by
1. adjusting CH2OS
2. adjusting VRMSOS
The offset error specification in the datasheet suggests that adjustment of CH2OS is always required for meaningful measurement results.