If you have previously uploaded a map trailer when you go to publish a new version it doesn’t show the previous trailer is there in the same way that the previous island image is there.
I’ve been re-uploading the trailer every new map revision that I publish but I wasn’t sure if this was necessary. It’s just that there is no visual indicator that the previous trailer will persist in the update.
I have an answer! You do not need to upload a new video or thumbnail. Your old one will persist. But you can always upload a new video or image if you want to.
You only need to upload a new video and thumbnail if you release a new version of the island.