FlatList with initialScrollIndex skips earlier items when list fits viewport

Description

If initialScrollIndex is set to a non-zero value and the list fits entirely on screen, items before that index are not rendered on Android.

You land at the correct index, but the items before it never appear and can’t be reached

Steps to reproduce

1. Render a short FlatList so all items fit in the viewport (no scrolling)
2. Set initialScrollIndex to something > 0
3. Provide getItemLayout

The provided expo snack has a complete demo example with trigger buttons.

React Native Version

0.84.1

Affected Platforms

Runtime - Android

Output of npx @react-native-community/cli info

System:
  OS: Windows 11 10.0.26200
  CPU: "(16) x64 AMD Ryzen 7 6800H with Radeon Graphics         "
  Memory: 4.72 GB / 15.25 GB
Binaries:
  Node:
    version: 23.5.0
    path: C:\Program Files\nodejs\node.EXE
  Yarn:
    version: 1.22.22
    path: C:\Users\Andrei\AppData\Roaming\npm\yarn.CMD
  npm:
    version: 11.9.0
    path: C:\Program Files\nodejs\npm.CMD
  Watchman: Not Found
SDKs:
  Android SDK: Not Found
  Windows SDK:
    AllowAllTrustedApps: Enabled
    Versions:
      - 10.0.26100.0
IDEs:
  Android Studio: Not Found
  Visual Studio: Not Found
Languages:
  Java:
    version: 23.0.1
    path: C:\Program Files\Common Files\Oracle\Java\javapath\javac.EXE
  Ruby: Not Found
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.84.1
    wanted: 0.84.1
  react-native-windows: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

There is no crash or thrown error in this case.

This is a rendering issue:

MANDATORY Reproducer

https://snack.expo.dev/@andyhoover/flatlist-initialscrollindex-bug-2026

Screenshots and Videos

Expo Snack の再現ケースから始め、initialScrollIndex がゼロ以外で、リストが viewport に収まり、getItemLayout が指定されている場合の Android における FlatList の動作を調査します。関連する React Native Android のエントリポイントを追跡し、そのうえで、初期インデックスが引き続き選択された状態で、前のすべての項目がレンダリングされ、到達可能なままであることを検証します。