Audio channel randomly shifted on Respeaker 6Mic array board

I am using ReSpeaker 6-Mic Circular Array kit for Raspberry Pi. It is mentioned in the “Wiki” that if you record using the following command
“arecord -Dac108 -f S32_LE -r 16000 -c 8 a.wav”.
You will get 8 channels in which last 2 channels will be empty because our kit only has 6 microphones.
But in my case, the location of these 2 empty channels keep on shifting randomly. Like sometimes channel 1 and 2 are empty, sometimes channel 3 and 4 are empty. I have also tried to record using “Audacity”, but observe the same behavior.
The behavior random channel shifting keeps on happening, even if I record for channels less than or equal to 6.
The correct sequence of channels are very important for my project. If anyone faced a similar issue, or know how to handle this problem, please let me know.