I'm receiving 0s in local costmap

Hi everyone, I’m following the course of The Construct about launching multiple turtlebots.
I’m able to run the project on melodic which was actually for Kinetic but doing some changes to the launch files I got it up and running. But the problem I’m facing rn is that I’m receiving 0s in the local costmap which is not the case when I run a single turtlebot. Besides local costmap, everything is working perfectly.

Please let me know if I should provide further details.