Kepware OPC UA Client Driver – Subscription Mode Fails to Recover After Communication Interruption with zenon OPC UA Server (Version 11)

Hi All,

We are facing an issue with OPC UA communication between a Zenon OPC UA Server (Version 11) and Kepware 6.18, where Kepware is configured with the OPC UA Client Driver to communicate with the Zenon system.

System Architecture:

• OPC UA Server: Zenon Version 11
• OPC UA Client: Kepware (OPC UA Client Driver)
• Communication: OPC UA
• Kepware Device Setting: Exception-Based Subscription Mode

Issue Description:

When communication between the Zenon system and Kepware is interrupted, the tags in Kepware transition to an Unknown quality state, as expected.

However, once communication is restored, the tags briefly transition to Good quality, but the actual tag values do not update. After a few seconds, the tag quality transitions back to Bad.

It appears that the OPC UA subscription is not recovering properly after the communication is re-established.

Observation:

We have tested the same configuration using both communication modes in Kepware:

1. Exception-Based Subscription Mode:
   • Communication interruption causes tags to transition to Unknown.
   • After communication is restored, tags briefly show Good quality.
   • However, tag values are not updated.
   • After a few seconds, tags transition back to Bad quality.
   • Normal communication does not recover automatically.
2. Poll Mode:
   • Communication interruption causes tags to transition to an abnormal quality state.
   • Once communication is restored, Kepware resumes reading the tag values normally.
   • Communication recovers automatically without any issues.

Our Question:

Has anyone experienced a similar issue with the Kepware OPC UA Client Driver when communicating with a Zenon OPC UA Server?

Could this be related to OPC UA subscription recovery, session reactivation, subscription transfer, or monitored item handling after a communication interruption?

Are there any specific Kepware or Zenon configuration settings that need to be checked to ensure subscriptions are properly re-established after a communication failure?

However, we have a concern regarding data integrity:

• In Poll Mode, if a tag value changes suddenly between two consecutive polling cycles, could that intermediate value be missed?
• Is there a possibility of data loss if multiple value changes occur between polling intervals?

Any suggestions, troubleshooting steps, or known fixes would be greatly appreciated.

Thanks in advance for your support!