I guess I found a bug today as I wanted to record a ros2 bag from simulated data.
All topics, that were already subscribed by other nodes e.g. rqt_image_view to view images, a pointcloud processing node that processed the lidar pointcloud etc., were not recorded in the rosbag.
I also tested this by just subscribing to the same image topics with two rqt_image_view windows, which had the same effect, that only the first could sucessfully subscribe to the image and the second did not show anything.
I can also reproduce the issue, when I start the simulation, then first subscribe to the image with rqt_image_view or RViz, then close the image viewer and try to subscribe to it again.
So it seems, that once a connection to a subscriber has been established, no more connections can be established.