Fill rate & request problem


I use MoPub that serve banner ads in my app . These ads are House ads and it display a custom image which is host in a host picture website.
I rode my stats and i saw REQUEST = 300 ; IMPRESSIONS = 190 ; FILL RATE = 63.33%
it looks like there is a problem between Request and impressions.
Do you think it’s due to my picture banner that is host in external website and is too longer to load ?
Or is it normal ?

Thanks you