Motor stuttering with roboCAN bus

I have 2 SBL2360T controllers on a roboCAN bus, 4 motors and a computer connected via the USB port on the controller.
As follow:


I am able to address all 4 motors and get them to spin a different speed, stop by sending serial commands via the USB port of the controller.

My issue comes on motor 1 of controller ID 2. Periodically the motor stops and ramps back up creating a stutter on only this motor out of the 4. The other 3 follow the commands without any issues.

I use the !G command to change the speed of the motors. I also disabled the Watchdog on both controller

Here is a log using Roborun+ plugged in to the other controller using USB to monitor the issue:

PS: same issue is observed without plugging in Roborun+ monitoring PC to the USB port of second controller.

As you can see, motor 2 spins up normally to the commands, motor 1 spins up but randomly, momentarily drops back down to zero creating a stutter.

Now for the strangest part, if I connect the Controller PC issuing the same commands to the controller with ID 2, motor 1 of controller ID 1 shows the exact same behaviour as motor 1 of controller ID 2 in the previous experiment showed on the Roborun+ log

 

Lastly, the configuration of both controllers is the same apart from the Node ID:
 
Why is motor 1 of the controller not taking commands via USB serial behaving strangely?
How can I fix this issue?