KB-2428 Start Process Smart Service Fails With Depth Guardrail Error APNX-1-4581-308 Stating Limit of 10 Instead of Documented Limit of 100

Symptoms

1. Processes fail at a Start Process node with a depth guardrail error. The following error appears in tomcat-stdOut.log:

   [Appian Work Item - ... : UnattendedJavaActivityRequest] ERROR com.appiancorp.process.engine.UnattendedJavaActivityRequest - An error occurred while executing activity: id=..., classname=com.appiancorp.process.runtime.activities.StartProcessSmartService4

   com.appiancorp.suiteapi.process.exceptions.SmartServiceException: userMsg[error.depthGuardrail.userMsg=The task sampleTask tries to instantiate a sub-process with depth greater than the limit of 10.] alertMsg[error.depthGuardrail.alertMsg=The task sampleTask tries to instantiate a sub-process with depth greater than the limit of 10.]

   ...

   Caused by: com.appiancorp.expr.server.environment.epex.exceptions.AutoscaledProcessGuardrailRuntimeException: com.appiancorp.suiteapi.common.exceptions.AppianException: The node sampleNode tried to instantiate a subprocess with depth greater than the limit of 10. (APNX-1-4581-308)

2. Error message indicates the depth limit is 10, but Appian documentation: Process depth protections states the limit should be 100 for processes without autoscale.
3. Process call chains reach depth 9 or 10, which is below the documented limit of 100 but exceeds the incorrectly enforced limit of 10.

Cause

In self-managed environments running Appian versions lower than 26.1, the default maximum depth for the Start Process Smart Service is incorrectly set to 10 instead of the documented limit of 100. The Sub-Process node maintains the correct maximum depth of 100.

This issue has been hotfixed via AP-3385 in Appian 26.1.

Action

Upgrade to Appian 26.1+.

Workaround

1. Add the following property to <APPIAN_HOME>/conf/custom.properties:

server.conf.processcommon.MAX_SUB_DEPTH=100

2. Restart the application server for the property to take effect.

Affected Versions

This article applies to Self-Managed environments running Appian 25.4 and earlier.

Last Reviewed: October 2026.