FlatList: initialScrollIndex broken in v0.16

[hizo]

The problem
initialScrollIndex prop on FlatList stopped working from v0.16

How to reproduce
Simplified test case: https://codesandbox.io/s/nifty-hopper-44ntf

Steps to reproduce:

1. open the above test case link
2. observe an empty list with a scrollbar on the right (no signs of attempted scroll - the scrollbar is at the top of the list)
3. scroll
4. observe all items render at this point, with the scroll starting at the top of the list, instead of the provided index in initialScrollIndex prop

Expected behavior
FlatList renders items starting from the correct index provided in initialScrollIndex prop and the scrollbar shows correct position.

Environment (include versions). Did this work in previous versions?

• React Native for Web (version): 0.16.3
• React (version): 17.0.2
• Browser: Google Chrome Version 90.0.4430.212

This worked in 0.15.x versions and below
Test case showcasing correct behaviour with rn-web v0.15.7: https://codesandbox.io/s/elegant-leaf-8yt3c

[hizo]

Any update on this please? @necolas

[sirpy]

not working also on 0.17
as a workaround it is possible to pass this method to the "ref" prop
where selectedFeedIndex is the initial item

const getFlatListRef = useCallback(
    flatList => {
      if (flatList) {
        flatList.scrollToIndex({ animated: false, index: selectedFeedIndex })
      }
    },
    [selectedFeedIndex],
  )