Downloaded Video Is not working

Hi There

Good Evening!!!!!!!!!!!!

I m using iphone 5s from last 11 months.six months ago I had captured the video and saved in Gallery but from last 2 months whenever I want to watch that video its shoving that video is not downloaded and than I am downloading the same video a message comes to my phone That "cannot Download Video there was an error downloading this video from your icloud photo library please try again later.'and same message came with other video too which I have got from "Whatsapp".

I would Like to request your good self that please look into this matter and suggest me what to do to avoid the same problem in future too.

Thanking you.

Denish Modi