I bought and downloaded Summerset last week. I have the latest High Sierra OS X.
The installer app started downloading the ~87 gig game but it stops downloading, or slows to a crawl, if the installer app is in the background. While it's downloading, if I switch to any other app, the speed of the download drops to almost nothing. If I switch the app back to the foreground, the speed picks back up to the max my connection gives me. You can see the speed in the installer itself go up and down just by switching between apps.
North America - PS4