Hi!
There was a thread in the past with a similar issue without solution.
The issue in my case is that the 48V Multiplus II always measures more than the real voltage of the system by about 2-3V. The connectors are ok, the BMV700 is always showing the reality, just a few meters from the Multi.
I can't think of any reason why the measured voltage can be more other than faulty equipment.
Any ideas?