Transmitter Disconnects and Will Not Reconnect

I have an Ignition install with the MQTT Transmitter module that will disconnect from the server and never reconnect. The log file reads out as if it is successfully connecting and trying to publish historical metrics but indicates that no subscriptions are available before losing connection and giving a "Failed to subscribe to TARGET elements error.

On the Ignition install with the Distributor and Engine modules I am getting a LWT BD sequence number is invalid warning and an Ugly error on networking error.

Does anyone have any ideas on what is going on here? All modules are on 4.0.8 and Ignition version 8.1.7. This installation is the only one with this issue out of the six total that we have. I’ve reset the module and the Ignition instances but I can’t find a cause since the setup is the same as the other installs. Really the only difference in setup that I can tell is that this is a full Ignition install vs Ignition Edge and this system does not use the same time sync server and is several minutes ahead of the rest of the system.

I believe we’ll need to look at logs in order to determine the root cause for the issue you’re seeing. Please reach out to support@cirrus-link.com with this issue and support will help to investigate/resolve it. Thanks.

In case anyone has a similar issue, this turned out to be an issue with MTU settings in the network. Our solution was to set the MTU down to 1350 at the device.

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This is something that we’ve seen more and more of on cellular networks. Large TCP packets (like in Sparkplug BIRTH messages) can result in fragmentation issues on certain cellular networks if MTU and MRU sizes are too big. Generally we would recommend contacting your cellular modem manufacture, driver vendor and/or cellular provider to find out recommended settings.

Common indications that this could be the issue are inconsistent behavior across Transmission refreshes, failure to consistently establish TLS sockets, and general inconsistent connection behavior especially with larger MQTT messages.