I hooked up rather redundant UtilityMeters / Combine Stats, in Order to extend/maintain it in the Future easily.
So with a Helper “Combine by Sum” i sum up utility-meters.
Then i set up another Utility Meter, with the former “Combine by Sum” as Source.
I need/want this, as i have technically two separate flats, and want to track consumption/cost individually.
However, for one of the Flats something went wrong, i suspect one of the underlying Sensors temporarily was reported unavailable. Resulting in the the “Combine Stats of Sensors” using the correct Unit of Measurement, while the Utility Meters using that Helper report no Unit of Measurement.
I already removed/re-added those Utility Meters, removed the History afterwards (Developer->Statistics), waited til the Value increased, restarted, but nothing fixed it.
Its driving me nuts 
What can i do to force it for the correct Unit?