Add persistence issue

Author: Pat Altimore

articles/iot-operations/troubleshoot/known-issues.md

@@ -321,6 +321,22 @@ If you create more than 70 data flows for a single data flow profile, deployment
 
 To work around this issue, create multiple data flow profiles and distribute the data flows across them. Don't exceed 70 data flows per profile.
 
+### The request persistence flag is not set for MQTT sessions created for data flow graphs (WASM)
+
+---
+
+Issue ID: 6415
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+---
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+Log signature: N/A
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+---
+
+When you create a data flow graph using the WASM, the MQTT session doesn't have the request persistence flag set. 
+
+To work around this issue, set MQTT broker **Retained messages** mode to `All`. For mor information, see [Configure MQTT broker persistence](../manage-mqtt-broker/howto-broker-persistence.md).
+
 ### Complex data might be flattened when enriching data in a data flow
 
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