mobile phone background video blurry but desktop is perfect

Hi,

I have added an MP4, 6 second looping, 10.5MB video to my home page on a website for a client. It's always blurry on mobile. Ive tried changing it from 25framespersecond to 50 (we are PAL here in Australia) and it just makes it worse. it stays blurry. I have contacted SquareSpace but they just said read the video upload specs. I have and it should work. our internet speed is minimum 50mbs. yes, this is not fast but fast enough for such a small video. my client runs 100mbs at his office. 

*its shot in 4k50fps but uploaded at 1080p

I have read online other people have had this problem. ive seen plenty of smooth videos running perfectly on mobile, web flow does a great job. 

maybe some of you know and can help? im not a proper website builder, have only used programmes like Squarespace. 

thank you! 

I have attached the video.