Why does my download restart

Either there were multiple updates or you need to reinstall it. Honestly, that shouldn’t happen unless your storage is full but I’ll take your word it’s not. Before re-installing make sure to verify your game’s files by clicking the options to the right of “Launch” and click verify and see if that fixes it first.

So i was downloading fortnite and it says i need an update which is cool i have plenty of space but when it “completes” instead of letting me play i have to re-download the update as if it were looping. Is there any way to fix it?
I am currently downloading High Sierra OS right now.