Output odom response does not match the step input

[Eswar1991]

We are trying to move the SUMMIT XL in a straight line in gazebo. The differential drive plugin for wheel joints is enabled and we gave a step input velocity to robot and observed the output response from \odom topic. There are sudden dips/ falls in the output responses for a small period of time. The output response and step input are shown below: Ideally, both the input and outputs must match, as we do the robot motion in a ideal simulation environment. Can anyone clarify why this discrepancy pops up?