[Arhowk]

Your analysis of the cause of the problem is incorrect. Motors will continue to go at the rate that they were previously assigned. If you were to place that motor set out of the while true loop, the motor should behave (rather it be jittery or smooth)

Speaking remotely, there are a few probable causes for what you are experiencing. Since your code runs multiple motors in the first scenario, is it possible a typo caused you to set the same motor twice with two different values? Is there nothing else being done to the motors in that scenario?

Are your communications totally perfect with 2-10ms ping and no packet loss? You could just be blocking the code that checks for proper router communication in the while true loop