Different totals in graph compared to singlestat

Hi, I have a graph and a singlestat panel showing me the standby power consumption of my heater. The query for both, the graph and the singlestat panel are the same, but shows me different totals. The graph shows me the correct total consumption, while the singlestat panel is wrong. I use grafana version 6.4.3 with influxdb version 1.7.9.

Any idea how I can fix this?

Here is the query I use:

SELECT non_negative_derivative(mean("counterReading")) AS "Counter Reading (Standby)" FROM "power" WHERE ("deviceName" = 'xxx') AND ("activePower" < 75) AND $timeFilter GROUP BY time($__interval) fill(none)

Singlestat panel is configured as shown here: