Can't delete Sample Image - not in folder

Hi,
I used the "Coworking Space" Index Site from Sp Pagebuilder Pro 5 and replaced the mp4. All fine so far, the wanted clip is showing even though not in a reply mode. What is more bothering is, a split second bevore the clip starts, a image of the Coworking Space shows up.

I habe checked all media files and there was nothing to delete.

Link https://alti-basler-dante.ch/abd25/

Thanks for checking and kind regards
Monika