And the culprit is

3F 04 7F 40 xx CS
DIA --> NAVE: Read adjustment value, Data= xx

It appears that when the diagnostic asks for this data from the nav unit, the request is also being interpreted (falsely) by the instrument cluster

Which would be a BMW bug

I think I will disable the ability to read the adjustment values for the time being, and then maybe add it back with some mechanism for the user to understand what is happening.