Process variables are not merging to workflow intermittently

Camunda 8 Topics
1

We are facing intermittently in production that in our workflow process variables are not merging to workflow hence correlation(message subscription) is not happening and workflow is not moving further.

Also observe the errors in Camunda ES index:

“errorType”: “EXTRACT_VALUE_ERROR”,

“errorMessage”: “”"Failed to extract the correlation key for ‘correlationkey’: The value must be either a string or a number, but was ‘NULL’. The evaluation reported the following warnings:

[NO_VARIABLE_FOUND] No variable found with name ‘correlationkey’“”"

OrderWorkflow
OrderWorkflow1587×663 90.5 KB

The code to merge process variables in java

client.newCompleteCommand(job.getKey()).variables(correlationKeyMap).send().exceptionally(throwable → {

			**throw** **new** RuntimeException("Could not complete job " + job, throwable);

		});

Is this possible that data are getting lost when we send command to zeebe somewhere?

Please advice, Thanks

2

Hi @camundatest,

This is a Problem classification - you’re experiencing intermittent correlation failures in production due to NULL correlation keys and missing variables.

Based on the error you’re seeing (EXTRACT_VALUE_ERROR with NULL correlation key and NO_VARIABLE_FOUND), here’s what’s likely happening and how to troubleshoot:

Root Cause Analysis

The error indicates that:

  1. Correlation key evaluates to null when the message subscription is activated
  2. The variable referenced in your correlation key expression doesn’t exist at that point in the process

Key Areas to Check

1. Correlation Key Configuration

  • Open your BPMN in Camunda Modeler
  • Check the Message definition used by your receive task/intermediate catch event
  • Verify the Correlation key field (e.g., =correlationkey)
  • Ensure the referenced variable exists and is non-null before the process reaches the message catch event

2. Variable Timing Issues

Since this is intermittent, the most likely cause is a race condition where:

  • Sometimes the correlation variable is set before the message subscription is created :white_check_mark:
  • Sometimes the message arrives before the variable is available :cross_mark:

To verify:

  • In Operate, inspect a failing process instance
  • Check if the correlationkey variable exists and has a value when the token reaches the message catch event
  • Look at the variable history to see when it was set vs when the subscription was created

3. Variable Merging Issues

For the “variables not merging” part:

  • Check Variable mappings on your message events
  • If you have output mappings configured, only mapped variables will be merged
  • Remove output mappings to merge all variables, or explicitly map the ones you need

4. Message Publishing

Ensure that:

  • Message name matches exactly between BPMN and your message publisher
  • Correlation key value sent from your client matches the process variable value
  • If using connectors, verify the Correlation key (payload) expression extracts the correct value

Immediate Actions

  1. Check your process timing - ensure correlation variables are set before message subscriptions
  2. Review variable mappings on your message events
  3. Verify correlation key expressions in your BPMN message definitions
  4. Monitor variable creation timing in failing instances

Need More Help?

To provide more specific guidance, could you share:

  • Your Camunda version
  • Environment (SaaS/Self-Managed)
  • The relevant BPMN snippet showing the message definition and correlation key
  • How you’re publishing the message (client code or connector configuration)

References:

Let me know what you find with these checks!