Generate velocity curve

Hi, I am a NUCLEO STM32H743ZI2 and I am trying generate one velocity curve with the register ARR. I'm using 3 stepper motors and firstly I tested the code with constant velocity but when I increment the velocity from 0 rpm to 2 rpm by 0.001 and the same trayectory, the execution of the three motros doesn't have synchrony. Does anyone know why it works fine with constant velocity and not with variable velocity? I think the error comes from constantly modifying the register ARR.

Thanks.