Spikes in RPM causing the ride to be bumpy

I am having an issue where I am running my motor off a 40V Ryobi battery and using a potentiometer to control the speed of the motor. When I am monitoring the VESC tool for check the RPM, I see that there are spikes every 15 seconds which reduces the speed (-50 from the regular speed) but the motor is back to its normal speed after a seconds to two. I checked it with 2 different fully charged Ryobi batteries and I am having the same issue. I am using VESC MKV6, Ryobi battery 40V 4Ah for my application. I will post the images shortly from the vesc tool

Probably because the bms limit in the battery.

What app setting you have?

Do you have brakes?

These are my app settings