rrd_fetch does not contain values from last update. why?

Question

I am storing information from temperature sensors in a rrd. I want to retrieve the values from a given timespan in php.

For data from the last 2 hours, I use this:

rrd_fetch($file, array("AVERAGE", "-s -2h"));

This is working. However, the last value that I can get via rrd_lastupdate($file); is not found in the data from rrd_fetch. How can I adapt my code so that the rrd_fetch call also contains data from the last update?

The rrd is setup like this in Python:

   rrdtool.create(
        RRD_FILE,
        "--start", "now",
        "--step", "300",
        "RRA:AVERAGE:0.5:1:288",
        "RRA:AVERAGE:0.5:12:336",
        "RRA:AVERAGE:0.5:288:365",
        "DS:temp:GAUGE:600:0:50")

And updated like this in a while loop:

while True:
    temp = get_value()
    data_rrd = "N:{0}".format(temp)
    try:
        rrdtool.update(file, data_rrd)
    except:
        print("Failed to write to RRD.")
    time.sleep(300)