Back-ground video in hero-slide will not load

Back-ground video in hero-slide will not load

I am building a new website in ZOHO-Site builder. I have chosen the 'Artsfine' template, which on the home-page has the 'hero-slide'. In the hero-slide it is possible to add back-ground video's, and on one of the slides it works fine, but on another the video just would not load! I have tried several formats, like mp4 or MOV and reduced the size to under 4 mb, but it just won't work! I don not know how to solve this. How can I proceed?