@bumptop Hi, I seem to have the same problem as you. My module is a SIM7670G, but otherwise I see precisely the same issue. Did you ever find a solution to this issue?
No matter what I do, the CMQTTSTART always returns ERROR. The same for all other MQTT related commands (with same exception as you).
I have tried many different execution orders, and I have read the application guides for the particular module, but nothing helps.