Chat - Blank space appears when sending a message while scrolling up

[jponikarchuk]

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Version Number: v9.3.60-0
Reproducible in staging?: Yes
Reproducible in production?: No
If this was caught during regression testing, add the test name, ID and link from BrowserStack: #85114
Email or phone of affected tester (no customers): n/a
Issue reported by: Applause Internal Team
Bug source: Pull Request QA execution
Device used: iPhone 13 iOS 26.3.1
App Component: Chat Report View

Action Performed:

1. Open the app
2. Open a chat with 100+ messages
3. While scrolling up, type a message and send it

Expected Result:

The newer messages should appear correctly whitout blank space

Actual Result:

Blank space appears when sending a message while scrolling up in chat

Workaround:

Unknown

Platforms:

• Android: App
• Android: mWeb Chrome
• iOS: App
• iOS: mWeb Safari
• iOS: mWeb Chrome
• Windows: Chrome
• MacOS: Chrome / Safari

Screenshots/Videos

Video.mp4

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[melvin-bot]

You have been assigned to this deploy blocker because you recently merged this PR: #85114

[melvin-bot]

💬 A slack conversation has been started in #expensify-open-source

[github-actions]

👋 Friendly reminder that deploy blockers are time-sensitive ⏱ issues! Check out the open `StagingDeployCash` deploy checklist to see the list of PRs included in this release, then work quickly to do one of the following:

1. Identify the pull request that introduced this issue and revert it.
2. Find someone who can quickly fix the issue.
3. Fix the issue yourself.

[OSBotify]

Investigation Summary - Frontend bug - PR 85114 - Migrate main chat to FlashList with inverted flag by @VickyStash - High confidence - Recommendation REVERT - PR 85114 replaced InvertedFlatList with InvertedFlashList. Bug is staging-only on iOS and Android native, caught in QA of this exact PR. Revert is safest. Assigned: @VickyStash @situchan @Julesssss @mountiny. Labels: DeployBlockerCash correctly applied, no changes needed. Root cause: MVCP race condition in FlashList inverted list on Android - patch 006 deferred rAF scrollTo races with scroll position reads, causing blank space when sending a message while scrolled up.