At the MQTT_ protocol in FX30 Cat-M, the mqtt subscribe operation has problem

I am working on an 'Ethernet to LTE ’ project by FX30 cat-m.
My environment for development

  • FX30, LTE-M/NB-IOT
  • Sierra Global SIM
  • sdk : FX30-CATM (Release R14.1.1.002 + Legato 19.11.5)
  • Firmware : FX30_WP77xx_full_R14.1.1.002-sierra-SWI9X06Y_02.36.06.00

I used the mqtt protocol library as below.

The basic operations of the mqtt protocol is fine.
However, sometimes when the broker send messages to the FX30, FX30 cannot subscribe to messages.
After that, when FX30 has publishing, that messages that have not been received are displayed as if they have subscribed at once.
It seems that subscribed contents that were not visible before the publish operation in FX30.
in my opinien, FX30 had received messages well, but display was failed. After that… when operation of publish, that all messages are displayed.
This doesn’t always happen, but it does happen quite often.

What is problem?
How can i solve this problem?

thank you.

Did you try local server which set up in
This can isolate network issue.

Also you can try other mqtt app here

thank you for your response

but, Maybe my case is difference that.

  1. ethernet → only gathering data.
  2. make JSON format in FX30
  3. LTE. CAT-M → MQTT protocol to broker. sub and pub mqtt data(JSON format)

I cannot find cause yet.

thank you.

I mean you set up the MQTT server in local PC to isolate the effect of LTE network

My Mqtt server is not Linux shell terminal)
There is Mqtt server another Server PC at another network.

that is why I say you can setup a MQTT server locally in
BTW, how to reproduce the issue?
What MQTT server are you using?
Can we install in it in Ubuntu PC (

@sphenix ,

Did you try the mosquitto for MQTT connection?

Let me know if you need any help


Pankaj Sant