You have noticed that if a custom uploaded thumbnail for a video is not selected to be displayed, it is no longer present when you try to re-edit the video. This causes you to have to re-upload the custom thumbnail when trying to edit the video after publishing it.
This is the expected product behavior. A custom thumbnail is only saved in the database if it is selected to be displayed.
When the video is in edit mode (or during the initial upload), all custom thumbnails are stored on the S3 bucket temporarily. If the custom thumbnail is selected as the video thumbnail then it is persisted after the edit session, if not then it is discarded.
The custom thumbnails are stored in AWS S3 during the video edit session but only the selected video thumbnail remains stored and its path saved on
JiveVideo table in the database. Unused, custom thumbnails are discarded as per design.