Distance - New rate is not reflected everywhere when split distance has a new rate

[jponikarchuk]

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Version Number: 9.3.17-0
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: #79099
Email or phone of affected tester (no customers): sdsjndosjonjisd@gmail.com
Issue reported by: Applause Internal Team
Bug source: Exploratory - Significant User Experience Deterioration
Device used: Mac 26.2 / Chrome
App Component: Money Requests

Action Performed:

Precondition:

• Workspace has at least two distance rates.

1. Go to staging.new.expensify.com
2. Go to workspace chat.
3. Create a distance expense.
4. Open the distance expense.
5. Click More > Split.
6. Click on any split row.
7. Click Distance > change the distance > Save.
8. Click Rate > select another rate > Save.
9. On split overview page, change the amount of the edited split (from Step 6).
   → Distance changes according to the edited amount (expected). Rate reverts to the original rate.
10. Click on the split row.
    → Distance and Rate field show different value than overview.
11. Click RHP back button.
12. Click Split.
    → Rate changes back to the selected rate.
13. Click on the edited split.
14. Click Amount.
    → Overview shows the old rate again.

Expected Result:

• When editing the distance rate when splitting distance expense, Distance and Rate in split overview page should match the split details page.
• The selected new rate should be reflected correctly.

Actual Result:

In Step 10, on split details page, Distance and Rate are different from the split overview page.
In Step 9, 12 and 14, the selected rate is not reflected everywhere. The old rate is seen in Step 9 and 14.

Workaround:

Unknown

Platforms:

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

Screenshots/Videos

1.mp4

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[melvin-bot]

You have been assigned to this deploy blocker because you recently merged this PR: #79099

[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.

[melvin-bot]

Triggered auto assignment to @trjExpensify (Bug), see https://stackoverflow.com/c/expensify/questions/14418 for more details. Please add this bug to a GH project, as outlined in the SO.

[OSBotify]

Investigation Summary

Classification: Frontend bug
Causing PR: #79099 - "Handle the Distance and Rate fields for splits" by @ZhenjaHorbach (High confidence)
Related Issues: None found

Recommendation: REVERT

This PR introduces a regression in split distance expense rate handling. The bug affects core split expense functionality and blocks the app deploy.

Labels: No label changes - keeping DeployBlockerCash (this is a frontend bug in an App PR, and it is staging-only)

Detailed Analysis

Evidence

The issue is reproducible on staging where PR #79099 is deployed, and the bug report was directly linked to this PR by melvin-bot. The issue states it's not reproducible in production (where this PR doesn't exist yet), confirming this is a staging-only regression.

Verification

PR #79099 modified the split expense handling logic, specifically adding distance and rate field support for split expenses. Key changes include:

• src/libs/actions/IOU/Split.ts - Added updateSplitExpenseField and updateSplitExpenseAmountField functions
• src/pages/iou/SplitExpenseEditPage.tsx - Added UI for editing distance and rate on individual splits

Root Cause

The bug is in the interaction between updateSplitExpenseField and updateSplitExpenseAmountField in src/libs/actions/IOU/Split.ts:

1. When rate is changed (lines 2281-2306 in updateSplitExpenseField):

   • The new rate is stored in splitExpenseDraftTransaction.comment.customUnit.customUnitRateID
   • Amount is recalculated based on the new rate
   • This works correctly

2. When amount is subsequently changed (lines 2342-2362 in updateSplitExpenseAmountField):

   • The function fetches the rate from the original transaction instead of the split's customUnit
   • Line 2342: const mileageRate = DistanceRequestUtils.getRate({transaction: originalTransaction, policy: policy ?? undefined});
   • This causes the previously selected rate to be ignored, reverting to the original rate

The issue is that updateSplitExpenseAmountField doesn't respect the rate that was set on the individual split expense. It should be using the rate from splitExpense.customUnit.customUnitRateID, not from the original transaction.

Impact

• User cannot successfully change the rate on split distance expenses
• Rate keeps reverting to original when amount is edited
• Distance and rate values become inconsistent between overview and detail views

[lakchote]

coming from #79099 cc @ZhenjaHorbach