Answer
Excess is a value that results from a master eGauge losing contact with certain remote registers, such as power values from a remote, secondary eGauge. It generally does not appear on eGauges without remote devices.
When a master eGauge re-establishes communication with a lost device, cumulative values (energy or kWh) on the master eGauge need to "catch up" to the remote device's cumulative values. This ensures that the data imported from the remote eGauge and the data measured by the master eGauge match at second granularity.
The master eGauge "catches up" to the remote device by adjusting the instantaneous (power or kW) values +/- a maximum of 10%, until the cumulative values (kWh) match. The amount difference between the master eGauge and it's remote register is considered excess.
This allows cumulative values like kWh (energy) to match between the master and remote device, even though there was a loss of communication. To summarize, when there is excess after communication loss, the instantaneous values on the master are adjusted +/- 10% until cumulative values match.