Hi,
It seems more a move_base configuration issue than rtabmap. I'll suggest to try this
standalone gazebo example and see what is going on. Use rqt_graph and look at turtlebot3 move_base configuration. For local costmap, they use the turtlebot lidar scan, but you could simulate a laser scan from your Zed's depth image using
depthimage_to_laserscan node.
cheers,
Mathieu