Navigation Error (Evaluator on channel 'frequency' hasn't sent messages for too long)

I’m using ROS Melodic and Isaac 2020.2 running on Ubuntu 18.04 on a NVIDIA Jetson Xavier. I’m trying to pull in data from a Velodyne Lidar to use with Isaac Navigation. I’m using the ROS velodyne driver and ROS bridge because I had issues with the Isaac Velodyne lidar. I’m getting the following error message from Isaac Navigation. What is this error message trying to say? What does “Evaluator on channel ‘frequency’ hasn’t sent messages for too long: 2.121073 > 2.000000” mean exactly?

2021-12-09 21:50:51.599 ERROR external/com_nvidia_isaac_engine/engine/alice/components/Codelet.cpp@229: Component ‘navigation.localization.localization_monitor/Monitor’ of type ‘isaac::monitor::Monitor’ reported FAILURE:

Evaluator on channel 'frequency' hasn't sent messages for too long: 2.121073 > 2.000000

2021-12-09 21:50:51.600 ERROR external/com_nvidia_isaac_engine/engine/alice/backend/event_manager.cpp@43: Stopping node ‘navigation.localization.localization_monitor’ because it reached status ‘FAILURE’
2021-12-09 21:50:51.684 ERROR external/com_nvidia_isaac_engine/engine/alice/components/Codelet.cpp@229: Component ‘navigation.localization.navigate_behavior/ParallelBehavior’ of type ‘isaac::behavior_tree::ParallelBehavior’ reported FAILURE:

2021-12-09 21:50:51.685 ERROR external/com_nvidia_isaac_engine/engine/alice/backend/event_manager.cpp@43: Stopping node ‘navigation.localization.navigate_behavior’ because it reached status ‘FAILURE’
2021-12-09 21:50:51.748 ERROR external/com_nvidia_isaac_engine/engine/alice/components/Codelet.cpp@229: Component ‘navigation.localization.localization_sequence_behavior/MemorySequenceBehavior’ of type ‘isaac::behavior_tree::MemorySequenceBehavior’ reported FAILURE:

a child failed

2021-12-09 21:50:51.748 ERROR external/com_nvidia_isaac_engine/engine/alice/backend/event_manager.cpp@43: Stopping node ‘navigation.localization.localization_sequence_behavior’ because it reached status ‘FAILURE’

The localization monitor is watching for messages on the “frequency” channel or topic and hasn’t seen one in over 2 seconds so it failued causing the appropriate updates in the behavior tree. The issues you’ve had with the Isaac SDK Velodyne lidar would also be interesting to know.