Corrent network traffic graphs

Hello community. I am polling snmp data from multiple deviceswith telegraf every 1m. I want to create a graph with the traffic measured in bps. Comparing to PRTG, most graphs seem correct, however some others dont. For example, these are two graphs of the traffic in the same link.

The query I use to get the data from Influx is the following:

SELECT non_negative_derivative(last("ifHCInOctets"), 10s) FROM "ciscoAsaInterface" WHERE ("sysName" =~ /^$sysname$/ AND "ifDescr" =~ /^$Interface$/) AND $timeFilter GROUP BY time($__interval) fill(null)

Do you have any ideas what am I doing wrong? I can provide more images with graph differences if needed.
Thanks a lot!