nRF9160 LTE-M network registration issue

[Fryderyk]

Hello,

we are experiencing an issue with devices based on nRF9160 using modem firmware lib 1.3.6 and nRF Connect SDK 2.5.3.

The problem manifests as a sudden inability to register to the LTE-M network. After successful initialization, the device waits for the
LTE_LC_EVT_NW_REG_STATUS event for approximately 15 minutes, but the event never occurs. Restarting the device does not resolve the issue.

The situation is only resolved after inserting a different SIM card, after which the device registers to the network correctly. The SIM card that did not work on our device was tested:

• on multiple units of our devices,

• in different locations,

and the issue was reproducible in all cases.

Importantly, the same SIM card was able to successfully register to the network only after being used in an nRF9160 DK with the Cellular Monitor v2.6.0 (modem firmware lib 1.3.5 )application. From that point on, the SIM card also started working correctly in our devices and the issue no longer occurs.

At the moment, due to the inability to reproduce the issue, it is difficult for us to debug the root cause, which is still unknown. We would like to ask:

• how we should further approach debugging this problem,

• what could be the potential causes of this behavior (e.g. SIM state, network behavior, modem state).

We are attaching a trace file captured using Cellular Monitor on the nRF9160 DK, recorded at the moment when the SIM card transitioned from a state in which it was unable to register to the network to a successful LTE-M network registration.trace-2026-01-16T11-26-16.868Z.mtrace

Thank you in advance for your support and guidance.

Best regards,

[Øyvind]

Hello, 

What SIM are you trying to connect with? Please note that first time initialization of SIM on network might be 15-30 minutes. 

only resolved after inserting a different SIM card

Was this with a SIM of same brand or different brand as well?

Kind regards,
Øyvind

[Fryderyk]

We have been using SIM cards from the same distributor in Poland (Orange). This was not the first initialization of these devices with this SIM card. Our devices were operating stably for about three months, after which we suddenly experienced the issues I described earlier.

Currently, we have lost connectivity on two additional devices, which are awaiting service due to their locations. We suspect they are experiencing the same problem. The devices stopped working within just a few days.

[Achim Kraus]

Fryderyk said:

Restarting the device does not resolve the issue.

Of course just a "guessing game" and work-around: die you try a "AT%XFACTORYRESET=0"?

AFAIK, the modem keeps some state related to the network and SIM (otherwise it would not restart that fast). Exchanging the SIM may reset that state, and so the device may be able to connect to the radio network again. A "AT%XFACTORYRESET=0" may also have a chance to reset such state. Maybe at least worth to try.

[Fryderyk]

Hi,

thank you — these are exactly the kind of suggestions we are looking for.

We have not tried AT%XFACTORYRESET=0 yet, but this is a very good hint and we will definitely test it as a potential recovery mechanism in our firmware.

Would it be possible to obtain (or is there available documentation for) the AT command sequence used by Cellular Monitor during initialization and network registration? We would like to analyze which actions are performed there that could be responsible for bringing the SIM card back to a working state.

[Achim Kraus]

I'm an other user. But maybe Øyvind from Nordic can help here.