Messages comes in the required frequency but sometimes not

Hi, I’m new to arudpilot and sitl so please bare with me.

I have a strange problem that i search over the internet and could not solve the problem.
I’m using ArduCopter, sitl and QGC

i’m writing the RAW_IMU message into a csv file and i’m setting the interval between messages 100hz
Most of the messages comes in the required frequency, but some messages comes in 4hz or 0hz

i tried changing --streamrate = -1 or 100 in the configuration file (which, is in docker).

I’m attaching zip file containg: python code, RAW_IMU csv file, and docker file that contains the configuration
Thank you. (88.7 KB)