net: lib: azure_iot_hub: Add warning about risk of reconnections

Add a warning in the Azure IoT Hub library about the known
connectivity issue with Azure IoT Hub when the device is not
reachable.
The issue is not limited to the Asset Tracker v2, so the
Known issues note is moved to the "Other issues" section to reflect
that. Suggested workaround added to the note.

Closes CIA-511.

Signed-off-by: Jan Tore Guggedal <[email protected]>

Author: jtguggedal

doc/nrf/known_issues.rst

@@ -113,12 +113,6 @@ Asset Tracker v2
 
 .. rst-class:: v1-8-0 v1-7-1 v1-7-0 v1-6-1 v1-6-0
 
-CIA-351: Connectivity issues with Azure IoT Hub
-  If a ``device bound`` message is sent to the device while the device is in the LTE Power Saving Mode, the TCP connection will most likely be terminated by the server.
-  Known symptoms of this are frequent reconnections to cloud, messages sent to Azure IoT Hub never arriving, and FOTA images being downloaded twice.
-
-.. rst-class:: v1-8-0 v1-7-1 v1-7-0 v1-6-1 v1-6-0
-
 CIA-463: Wrong network mode parameter reported to cloud
   The network mode string present in ``deviceInfo`` (nRF Cloud) and ``dev`` (Azure IoT Hub and AWS IoT) JSON objects that is reported to cloud might contain wrong network modes.
   The network mode string contains the network modes that the modem is configured to use, not what the modem actually connects to the LTE network with.
@@ -253,6 +247,14 @@ NCSDK-10106: Elevated current consumption when using applications without :ref:`
 
   **Workaround:** Enable :ref:`nrfxlib:nrf_modem`.
 
+.. rst-class:: v1-8-0 v1-7-1 v1-7-0 v1-6-1 v1-6-0
+
+CIA-351: Connectivity issues with Azure IoT Hub
+  If a ``device-bound`` message is sent to the device while it is in the LTE Power Saving Mode (PSM), the TCP connection will most likely be terminated by the server.
+  Known symptoms of this are frequent reconnections to cloud, messages sent to Azure IoT Hub never arriving, and FOTA images being downloaded twice.
+
+  **Workaround:** Avoid using LTE Power Saving Mode (PSM) and extended DRX intervals longer than approximately 30 seconds. This will reduce the risk of the issue occurring, at the cost of increased power consumption.
+
 nRF5
 ****
 

doc/nrf/libraries/networking/azure_iot_hub.rst

@@ -17,6 +17,11 @@ When the device provisioning is complete, the library automatically connects to
 The library also has integrated support for Azure FOTA.
 For more information on Azure FOTA, see the documentation on :ref:`lib_azure_fota` library and :ref:`azure_fota_sample` sample.
 
+.. important::
+   If the server sends a device-bound message when the device is unavailable for a period of time, for instance while in LTE Power Saving Mode, the server will most likely terminate the TCP connection.
+   This will result in additional data traffic as the device has to reconnect to the server, which in turn requires a new TLS handshake and MQTT connection establishment.
+
+
 .. _prereq_connect_to_azure_iot_hub:
 
 Prerequisites for connecting to Azure IoT Hub