Negative battery

Any ideas why we are seeing negative battery discharges in the energy graph? Day before absolutely normal…

Not sure if the same thing, but I saw negative "solar to home" and negative "battery to home" values for one particular day.

GivSuport said it's likely due to a powercut I had that day (not a long powercut). They say any interruption to the data - power or internet connectivity could cause something like this.

Seems a bit weird, but so far only seen it once.