All Images are not downloading in background

I imported products from shopify succesfully and images were being imported in background
but dont why why suddenly Images stopped importing. I kept that tab opened and when i am refreshing again its asking me to begin import i am clicking that begin import but still it stopped and not importing images of more products leaving so many products without images.
also when i refresh page then again there is an option to resume import but i click on it and its just stuck at 1 point.
I tried to do this all over again but i realized that it gets stopped at 1 specific point of images
after those images it don’t import more images leaving many products without images.

How to resolve this issue?