Orion XS 12V/12V 50 showing Wrong Input voltage

After Installation i recognized that my Orion XS is showing an Input voltage in the Victron App 0.4V lower compared to a value from a professional voltmeter at Pins IN/GND. The system is not charging (Off) while measuring the voltage.

Accordingly the device stopps charging to early and is Not working correctly.

(The Input voltag is at 13V Level because engine just stopped 5mins earlier)

Setup: Lead-acid Akku at IN / LiFePO at OUT.

GND common

Any ideas?