Parallel branch error – Issues with parallel branches in the flow, often due to conflicting data.

Power Automate allows the use of parallel branches to execute multiple actions simultaneously. However, when a Parallel Branch Error occurs, it usually indicates:

Conflicting data updates between parallel actions.
Race conditions, where one action finishes before another, causing unexpected failures.
Actions depending on each other incorrectly, leading to execution issues.

This guide explains:
🔹 Common causes of Parallel Branch Errors
🔹 How to diagnose and fix the issue
🔹 Best practices to prevent errors when using parallel execution

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Step 1: Understanding Parallel Branch Execution in Power Automate

What Are Parallel Branches?

Parallel branches in Power Automate allow multiple actions to execute at the same time instead of sequentially.

Example of Parallel Execution:
🔹 Branch 1: Retrieves data from SharePoint.
🔹 Branch 2: Sends an approval email at the same time.

However, issues arise when:
The same data is modified in both branches, causing conflicts.
One branch finishes later than expected, creating dependency issues.
Both branches write to the same variable, leading to incorrect values.

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Step 2: Diagnosing the Parallel Branch Error

2.1. Check Flow Run History for Failures

1. Open Power Automate (https://make.powerautomate.com).
2. Navigate to My Flows → Select the failing flow.
3. Click Run History and open a failed run.
4. Identify where the parallel branches start and end.
5. Check if any actions failed due to conflicts or missing data.

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Step 3: Fixing the Parallel Branch Error

3.1. Prevent Conflicting Data Updates

Problem: Two branches try to update the same data source (e.g., SharePoint, Dataverse, SQL) at the same time.

Solution:

• Ensure that each branch updates different records or fields.
• Add a delay to avoid simultaneous updates.
• Use a sequential dependency instead of parallel execution when necessary.

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3.2. Prevent Race Conditions in Dependent Actions

Problem: One branch depends on another, but they run simultaneously, causing missing or incorrect data.

Solution:

• Use the “Configure Run After” setting to make one branch wait for the other.
• Use a “Wait Until” action in one branch to ensure the other finishes first.

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3.3. Avoid Writing to the Same Variable in Both Branches

Problem: Both branches modify the same variable, causing inconsistent results.

Solution:

• Create separate variables for each branch, then merge results later.
• Use the “Append to Array Variable” action instead of overwriting values.

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3.4. Synchronize Data Updates Using a Lock Mechanism

Problem: One branch updates a record while another tries to read it, leading to conflicts.

Solution:

• Introduce a status flag (e.g., “Processing”, “Completed”) to prevent updates on the same record at the same time.
• Use a “Get Item” action before updates to check if another process has changed the data.

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3.5. Use Sequential Execution Instead of Parallel Branching (If Needed)

Problem: Parallel execution isn’t necessary and causes unnecessary complexity.

Solution:

• If one action depends on another, keep them in a single sequence instead of using parallel branches.
• Use “Scope” to group actions together and control execution order.

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Step 4: Preventing Future Parallel Branch Errors

✅ 4.1. Always Review Dependencies Before Using Parallel Execution

• Use parallel branches only when actions don’t depend on each other.
• If an action requires data from another branch, restructure the flow.

✅ 4.2. Use Separate Variables for Each Branch

• Avoid modifying the same variable in different branches.
• Merge values after parallel execution if needed.

✅ 4.3. Add Delays or Synchronization Mechanisms

• Use “Delay” or “Wait Until” actions to prevent conflicts.
• Implement a status flag (e.g., “Pending”, “Processing”) before updating records.

✅ 4.4. Monitor Flow Performance & Set Alerts

• Regularly check Run History for execution timing issues.
• Set up alerts for unexpected parallel execution failures.

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Step 5: Setting Up Alerts for Parallel Execution Failures

To detect parallel execution issues early, set up a notification:

1. Add a “Condition” action before an update.
2. If the expected data is missing (due to race conditions), send an email alert.
3. Example: If outputs('GetItem') is empty → Send alert email "Parallel Execution Conflict Detected!"