onEnter triggered in Chrome, but not on iOS (if window is scroll ancestor)

I was able to implement `react-waypoint` successfully in combination with a `div` that had been set to `overflow-y: scroll`. I've set the bottom offset to 300 and am reacting to the `onEnter` event. This combination works just fine.

However, I then wanted to use the same approach on a scrolling page, without a scrollable `div`, i.e. just the regular browser window. `react-waypoint` picks up the window as its scroll ancestor, and everything seems to be setup correctly. It works fine under Chrome on macOS. If I try to scroll on an iOS device, however, nothing happens. If I enable `debug` mode, only the scroll ancestor and its dimensions are being printed out, but nothing happens if I start scrolling. It confuses me, because this scenario seems to be the simpler scenario to me.

What might go wrong here?

Start by reproducing the issue on an iOS device with the browser window as the scroll ancestor, comparing it with Chrome on macOS and checking the debug output. Done means scrolling on iOS triggers the expected onEnter event in this configuration.

Written by the indexing model from the issue text.