You are using Collectd 4, which is deprecated by CGP. Graphs like df and interfaces may be incomplete.
FreeSun-Gaswerksiedlung-4

iwinfo

"-l" "0" "-w" "800" "-h" "350" "-t" "iwinfo signal_power (wlan0-dhcp-5)" "-s" "e-28800" "DEF:min_1d775834_raw=rrd.php?path=FreeSun-Gaswerksiedlung-4%2Fiwinfo-wlan0-dhcp-5%2Fsignal_power.rrd:value:MIN" "DEF:avg_1d775834_raw=rrd.php?path=FreeSun-Gaswerksiedlung-4%2Fiwinfo-wlan0-dhcp-5%2Fsignal_power.rrd:value:AVERAGE" "DEF:max_1d775834_raw=rrd.php?path=FreeSun-Gaswerksiedlung-4%2Fiwinfo-wlan0-dhcp-5%2Fsignal_power.rrd:value:MAX" "CDEF:min_1d775834=min_1d775834_raw,1,*" "CDEF:avg_1d775834=avg_1d775834_raw,1,*" "CDEF:max_1d775834=max_1d775834_raw,1,*" "LINE1:avg_1d775834#ff0000:value" "GPRINT:min_1d775834:MIN:%5.1lf%s Min," "GPRINT:avg_1d775834:AVERAGE:%5.1lf%s Avg," "GPRINT:max_1d775834:MAX:%5.1lf%s Max," "GPRINT:avg_1d775834:LAST:%5.1lf%s Last\l"