video cover not working on mobile

Hi ,

I am using Twenty Seventeen (HEB version wordpress – newest version) and i’ve putted a nice video on my site header (media headline video) , it works great on desktop computers but for some reasone it doesn’t work on mobile – can any one tell me why (when i do “mobile preview on my computer it works , but not on the mobile itself?

My site is : https://www.im-online.co.il if you need to see it yourself.

I need your help with taht pleaseeee

Another small qestion: if you look a bit under the video header you can see the words (title of page) :
?? ?? ??? ???
Can you tell me where can i make the text larger/bigger?

Many thanks!!