aggregateWindow for incomplete timeframes

i am using influx 2.0 oss and want to achieve the following:
aggregate data per month

this should be an easy task, but i only get data for completed months.
e.g. i have data from 2021-03-09 until today. with my query i only get data for march. what i want is to get data for the current month displayed as well. that doesn’t work. any hint?

my query:

rawSeries=from(bucket: "test")
|> range(start: -1y)
|> filter(fn: (r) => r["_measurement"] == "data")
|> filter(fn: (r) => r["_field"] == "value")
|> filter(fn: (r) => r["type"] == "Export")
|> aggregateWindow(every: 1d, fn: first, timeSrc: "_start")
|> difference()
|> timeShift(duration: -2h1s)
namedSeries = rawSeries
    |> map(fn: (r) => ({_value:r._value, _time:r._time,_type:r.type, _field:"erzeugte Leistung "+r.type}))
namedSeries |> yield()

but this gives me just one row:

erzeugte Leistung Export

what am i doing wrong?

I think it is due to the fact that first is a selector and not an aggregator. If you try with mean, does it work as expected? obviously this is not what you want but it could bring you to the right path. If this is the issue you could follow what written here: aggregateWindow with create empty inconsistent behavior · Issue #3428 · influxdata/flux · GitHub

no, with “mean” it looks the same. only difference is further rows in the past.
but april is still not shwoing up.