The timeline previews operation creates preview images for the given track that can be shown when hovering above the timeline. It will generate the in image-count specified number of preview images, that will all be saved in one large image file. You can use the source-flavor to specify for which video the preview images will be generated.
In the engage player only the preview images of one video are shown (the first that is found), so to make sure the correct preview images are shown, better generate them only for one video.
But wildcard flavor selection is used
Which on running the workflow produces multiple timelinepreviews for each of the flavors even though only one is to be used - would be better to implement in code something like compose's