No message published to ROS Melodic from clearpath(Indigo)

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Currently we have a clearpath ridgeback running Ubuntu 14.04(Indigo) that is connected to a remote PC running Ubuntu 18.04 (Melodic).

Currently I'm able or not able to do the following:

1) running rostopic list on my remote PC, I'm able to see all the topics being published by ridgeback; However, I'm not able to rostopic echo any of the above topics on my remote PC. For example, when I run

rostopic echo -c tf

There is no response on my remote PC. However, if I run the same command on my ridgeback, I can see the tf topic is being printed out.

2) When I run rostopic echo $ANYTOPIC$ on my remote PC and run rostopic info $ANYTOPIC$ on the ridgeback, I can see there is a new subscriber created for my remote PC to subscribe $ANYTOPIC$;

3) I can publish info (simple rospy publisher tutorial) from my remote PC to the ridgeback robot and the ridgeback can successfully subscribe to it and print it out; The ridgeback can publish info and my remote PC is able to subscribe to it and print it out. The problems only exist for the topics that are being published at the start-up of ridgeback.

5) This problem doesn't happen until I upgraded my PC to Ubuntu 18.04.

Can anyone provide a few thoughts?

Thanks.