Spend - After adding several existing expenses offline, previous report shows incorrect amount

[jponikarchuk]

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Version Number: 9.3.65-0
Reproducible in staging?: Yes
Reproducible in production?: N/A - new feature, doesn't exist in prod
If this was caught during regression testing, add the test name, ID and link from BrowserStack: #85225
Email or phone of affected tester (no customers): ibellicotest+2250@gmail.com
Issue reported by: Applause Internal Team
Bug source: Exploratory - Significant User Experience Deterioration
Device used: Motorola MotoG60 / Android 12 (Hybrid app) - Windows 11 / Chrome
App Component: Search

Action Performed:

Prerequisite: Account has at least one workspace.

1. Open the staging.new.expensify.com website.
2. Open any workspace chat.
3. Create three manual expenses on the same report.
4. Create an empty report.
5. Navigate to "Spend" > "Reports"
6. Turn off internet connection.
7. Open the report created on step 4.
8. Click on "Add Expense" > "Add existing expense"
9. Select all the expenses from the remaining report and add them.
10. Return to "Reports"
11. Note that previous report, that is now empty, doesn´t show "0.00" as amount.
12. Turn on internet connection.
13. Note that now amount is correctly updated.

Expected Result:

After adding all the expenses from a report to another one while offline, first report should automatically display "0.00" as amount.

Actual Result:

After adding several existing expenses to a report while in offline mode, amount on previous report is not correctly updated.

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: #85225

[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

Classification: Frontend bug
Causing PR: #85225 - "Feat: Change Add unreported expense to Add existing expense in a report" by @nyomanjyotisa (High confidence)
Related Issues: #84130

Recommendation: REVERT

PR #85225 expanded the "Add existing expense" flow to also surface expenses from open Draft reports (not just purely unreported/selfDM expenses). This exposed a bug in the changeTransactionsReport optimistic total calculation logic in src/libs/actions/Transaction.ts: when multiple expenses are moved from the same source Draft report, only the first transaction's amount is deducted from the source report's optimistic total, and subsequent deductions are silently dropped. The result is that the source report's displayed amount does not update to "0.00" after all expenses are moved away while offline. Before this PR, the flow only handled truly unreported transactions (no backing oldReport in Onyx), so the stale-total code path was never triggered for a real source report.

Assigned: @nyomanjyotisa (PR author), @puneetlath and @sobitneupane (approving reviewers) from highest-confidence causing PR only
Labels: DeployBlockerCash kept (frontend App PR is the cause). No label changes made.

Detailed Analysis

Evidence

• The issue body itself links PR Feat: Change Add unreported expense to Add existing expense in a report #85225 as the regression test source (the "If this was caught during regression testing" field).
• PR Feat: Change Add unreported expense to Add existing expense in a report #85225 is present in the StagingDeployCash checklist for version 9.3.65-0, confirming it is part of this staging release and was not in production.
• The bug is marked "Reproducible in staging? Yes" and "Reproducible in production? N/A - new feature, doesn't exist in prod" - consistent with the feature being introduced by PR Feat: Change Add unreported expense to Add existing expense in a report #85225.
• The melvin-bot comment on the issue explicitly assigned the PR author @nyomanjyotisa because of PR Feat: Change Add unreported expense to Add existing expense in a report #85225.

Verification

• Affected file: src/libs/actions/Transaction.ts (the changeTransactionsReport function, specifically the updatedReportTotals accumulation loop around lines 1206-1226).
• Affected UI file: src/pages/AddExistingExpense.tsx (renamed and expanded from AddUnreportedExpense.tsx by PR Feat: Change Add unreported expense to Add existing expense in a report #85225).
• PR Feat: Change Add unreported expense to Add existing expense in a report #85225 does not directly modify Transaction.ts, but it changed src/pages/AddExistingExpense.tsx and src/selectors/Report.ts to allow Draft-report expenses to be selected, which routes them through the changeTransactionsReport code path with a real source report ID.

Root Cause

In changeTransactionsReport (Transaction.ts), the logic that accumulates the optimistic total for the source (old) report contains a bug at line 1216:

updatedReportTotals[oldReportID] = updatedReportTotals[oldReportID] ? updatedReportTotals[oldReportID] : updatedReportTotal;

updatedReportTotal at line 1207 is computed as oldReport.total ± transactionAmount, where oldReport.total is always the original report total from Onyx, not the running accumulated total. After the first transaction is processed for a given source report, updatedReportTotals[oldReportID] is set, so the ternary never updates it again for subsequent transactions from the same report. Only the first transaction's deduction is applied; all remaining deductions are lost.

Before PR #85225, this code path was unreachable for a real source report because the "Add unreported expense" flow only picked up transactions with reportID === '' or CONST.REPORT.UNREPORTED_REPORT_ID. These transactions have no backing oldReport in Onyx, so the if (oldReport) block (line 1209) was skipped entirely and the total was simply marked stale. PR #85225 introduced openExpenseReportIDsSelector and used it in getEligibleTransactions to also surface expenses from open Draft reports, giving them a real oldReport. When a user selects all expenses from such a Draft report and adds them while offline, the accumulated total deduction is wrong and the source report does not display "0.00".