sim time stops when echo laserscan/data

[ronnic4280]

Hi, we are using the Robtnik Summit XL for the competition. While testing in the virtual maize field an trying to subscribe to rostopic echo /robot/front_laser/scan , we'll get the message: "WARNING: no messages received and simulated time is active. Is /clock being published?" and the simulation time in Gazebo pauses. I won't get the issue while testing on plain ground or in different worlds. I don't know where to seach for a solution, it seems like this is a issue relating to the virtual maize field. Has anybody an idea how to solve ist?

I'm using ros melodic on ubuntu 18.04