NB-IoT: inconsistent results

[techykermit]

Hi everyone! Currently working on testing PyCom NB-IoT support for our product. However, compared to CAT-M1, I'm experiencing much more unstable firmware and a much more unstable connection. The latter could be due to the network operator - in contact with their support team. On the other hand, their coverage in the testing area is said to be "excellent coverage". And outside bad connection (as in sometimes attaching times out (with a timeout of 30 seconds) and sometimes the device can sync NTP time but not upload to our MQTT server (NTP is done before the MQTT server, so I assume it loses connection), the LTE() API seems really unstable with NB-IoT because I can not get it to detach the LTE modem. Often when trying to detach LTE, I get OSErrors such as Modem connection failed and LTE modem version not read. This is seen on two separate PyCom devices after erasing and reflashing them too. Sometimes, it connects just fine.

Using the latest available NB-IoT firmware (41019) flashed using the NB-41019.dup file over UART. How can I debug why the connection, including the API, is so unstable? I have followed the LTE troubleshooting guide. Most slow connections seem to take the most time on WAIT_RSSI when connecting (when sending AT!="fsm"), but this is yet to be verified.