Got it. I added the old/default presets back, but first I had to delete the ones I created and the s3bubble thumbnail preset otherwise did not want to add all of the default ones. It looked like there was not enough space available for more presets. At first showed only the default presets, but now it it shows the default presets on top and than the system defined HLS presets underneath. With the default presets back I was able to convert an HD video, including the thumbnail previews for the timeline.
Thanks for the quick respond as I convert videos on daily basis. I also have to commend you on the new improvements. s3buble is getting way more sophisticated.