I got it working in Grafana by increasing the relative time in the query options. Works for those graphs where the last value is used.
I assume it will not work for graphs where the average of for example the last day is shown and value did not change in that last day.
So I would still be interested in ideas on how to get that flowcard “Write measurement … as number…” to work 
My expected behaviour of that flowcard is that any value will be written to the InfluxDB itself, also if the value is the same as the last written value.
