iotc.sendTelemetry(message) returns randomly error 4

[e1614331TU]

I'm working on a project with iot central based data logging and the connection to the internet is done via a UMTS stic. Data is collected and stored locally until there is good signal strength, then all the collected data is sent to the iot central in a loop.

The issue is that after some messages
iotc.sendTelemetry(message)
returns code 4, connection refused.
After all collected messages I disconnect from iotc and reconnect again in the next cycle. Only some loops and some messages fail to send.

Does someone have any idea to fix this or experienced similar behavior?

[dmitriyteteruk]

There are several limits in IoT Central - message size, # of messages per device and # of messages per second that IoT Hub (that is working in the back end) can absorb.
Could you please share size of message and # of messages that you are sending and during which period of time?
BTW. Error #4 = MQTT_ERR_NO_CONN = 4 it looks like no connection.
Also you can use
class IOTLogLevel: IOTC_LOGGING_ALL = 16
to see all logs.