BlueROV2 auto mode issues with Gazebo

Software Sim setup:
Linux Ubuntu 18.04
Gazebo 9

Just got my setup running with QGC ArduSub and Gazebo. First I tested it using manual mode with a joystick connected and the bluerov movement looked appropriate on both QGC and Gazebo. Next I added a survey pattern in QGC to try the auto mode. When running this mission I’m seeing unpredictable behavior. I would expect the bluerov to move forward toward the next waypoint, which is the behavior I see when running this mission without Gazebo. With Gazebo in place, however, the bluerov movement becomes unpredictable. The yaw is constantly changing and there are times when the bluerov moves way off track before correcting back toward the next waypoint. Also I see cases where the bluerov goes off track and gets into what looks like a repeating circle pattern and doesn’t recover from this.

I’m looking for help to find the cause of this behavior. Can someone point to what messages I can look at to determine where things start to go wrong ? Are there parameters that I can adjust to see if behavior changes? Please let me know if you need additional info.