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We recommend accessing the server through the UAExpert tool to verify endpoints and inspect node structures.
This assumes that you have first run the configuration tool as described in the configuration settings.

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Connection and certificate issues

If the extractor is unable to connect to the OPC UA server or maintain a secure session, try these solutions.
Do not leave source.auto-accept: true or source.ignore-certificate-issues: true enabled in production. These flags disable certificate validation and expose telemetry and credentials to interception. Use them only for short diagnostic tests while you set up certificate trust. See Configure SSL certificates and proxy settings for extractors.
If you get the error message Unable to connect to discovery server, make sure that you have specified the correct endpoint-url in the configuration file and that it’s possible to connect to the server from where the extractor is running.Solution:
  1. Confirm endpoint-url in the configuration file.
  2. From the extractor host, connect with UAExpert to verify network reachability.
Cause: The username or password in the configuration file or environment variables does not match what the OPC UA server expects.Solution: Verify the credentials in the configuration file or environment variables, then restart the extractor.
Cause: The OPC UA server does not trust the extractor’s client certificate. OPC UA uses mutual server/client certificate validation, so the connection is rejected.Solution:
  1. Move the extractor’s client certificate into the OPC UA server’s trusted certificate store.
  2. For a short connectivity test during initial setup, you can temporarily set source.auto-accept: true in the configuration file, then set it back to false. See the warning in Connection and certificate issues.
For comprehensive certificate and proxy guidance across runtime environments, see Configure SSL certificates and proxy settings for extractors.
This typically occurs if the server can’t handle a high load. Try to inspect what the extractor was doing as it crashed, then reduce source/browse-nodes-chunk, source/browse-chunk, source/attributes-chunk, or source/subscription-chunk in the configuration file.Solution:
  1. Reduce chunk sizes in config.yml: reduce source/browse-nodes-chunk, source/browse-chunk, source/attributes-chunk, or source/subscription-chunk.
  2. Increase source/keep-alive-interval.
Cause: The server certificate is signed with SHA1. The extractor treats SHA1 certificates as insecure and rejects them by default.Solution:
  • Update the server certificate to use SHA-256.
  • As a temporary diagnostic workaround only, set <RejectSHA1SignedCertificates>false</RejectSHA1SignedCertificates> under SecurityConfiguration in opc.ua.extractor.Config.xml, or set source.ignore-certificate-issues: true in config.yml. See the warning in Connection and certificate issues.
Cause: The server certificate key length is below the required security minimum.Solution:
  • Increase the key length of the server certificate.
  • Alternatively, adjust MinimumCertificateKeySize under SecurityConfiguration in opc.ua.extractor.Config.xml, or set source.ignore-certificate-issues: true as a temporary diagnostic workaround only. See the warning in Connection and certificate issues.
Cause: The server certificate lacks the data-encipherment usage flag required by the OPC UA standard.Solution: Reissue the server certificate with standard data encipherment key usage flags, or set source.ignore-certificate-issues: true as a temporary diagnostic workaround only. See the warning in Connection and certificate issues.
Cause: The secure channel was terminated because of a server-side session timeout, network interruption, certificate expiration, or server restart.Solution:
  1. Check the OPC UA server logs for session disconnect reasons.
  2. Increase session-timeout and keep-alive-interval in the extractor configuration file.

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Browse and hierarchy issues

If the extractor encounters errors when traversing the server hierarchy or discovering nodes, try these solutions.
Cause: Server-side resource constraints or concurrency limits fail when the extractor browses a large node tree.Solution: Reduce the browse load on the server:
  • Set browse-chunk: 100 and browse-nodes-chunk: 100 in the configuration.
  • Set max-parallelism: 1 and max-node-parallelism: 1 to serialize queries.
Cause: The OPC UA server’s response exceeds message encoding limits because the namespace is large or a single response returns too many child nodes.Solution:
  1. Reduce browse-chunk and browse-nodes-chunk in config.yml (for example, down to 5 or 10).
  2. If using the .NET extractor, increase message buffer limits in opc.ua.extractor.Config.xml:
    • MaxStringLength
    • MaxMessageSize
    • MaxByteStringLength
    • MaxArrayLength
Cause: The server invalidated browse continuation points after a nightly restart, a maintenance window, or a short session continuation timeout.Solution:
  1. Reduce browse-nodes-chunk and browse-chunk to complete browse operations faster within single sessions.
  2. Set max-parallelism: 1.
  3. Set ignore-continuation-points: true in the configuration to re-initiate browse queries when continuation points become invalid.

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Bad or missing data

If the extractor is unable to retrieve data, skips variables, or receives data in the wrong format from the OPC UA server, try these solutions.
Cause: The server has no mappable variables, string or non-scalar types are filtered out, or root-node and filter settings omit the nodes.Solution:
  1. In UAExpert, confirm that variables appear as green labels.
  2. Try setting extraction/data-types/allow-string-variables to true.
  3. If time series are still missing, check their dimensions. By default, the extractor requires variables to be scalar or fixed-size 1D arrays. Try setting extraction/data-types/unknown-as-scalar to true if variables have ValueRank equal to Any or OneOrMoreDimensions.
  4. Verify that the variables are not excluded by filters or omitted root node configurations.
Cause: The extractor infers data types from server definitions, and some variables are missing type metadata.Solution:
  1. Set extraction/data-types/auto-identify-types to true.
  2. Set extraction/data-types/null-as-numeric to true to treat variables with null DataType as numeric (only do this if you are certain none of these should be strings).
Cause: The extractor maps OPC UA variables to time series and properties to metadata. The server represents some metadata as variables.Solution: Use extraction/transformations in the configuration file to explicitly select and remap specific variable nodes to metadata.
Cause: The extractor requires scalar values or fixed-size arrays by default, so it skips variables with undefined array dimensions.Solution: Set extraction/data-types/unknown-as-scalar: true to treat dynamic or unspecified arrays as scalar values. You can also disable estimate-array-sizes to reduce startup evaluation overhead.
Cause: Historical backfill queries stale NodeIDs. This can happen if the raw node buffer skips node re-discovery after structural changes on the source server.Solution:
  1. Disable raw-node-buffer in the configuration file to force fresh node discovery.
  2. Clean up stale historical state in the CDF staging area if needed.
Last modified on August 20, 2026