Help with LTE connection after loss of connection

[AnnaQ]

We have noticed that several of our nRF9160 in production have problem with reconnecting to the LTE-M network after temporarily losing connection. We have tried reproducing this issue by deactivating the sim for about 10 seconds and then activating it again. After the default six retries it gives up and stop trying to reconnect to the network. the only way we can achieve a connection is if we do a sys_reboot() or a hard reboot with watchdog. Why is the reconnect attempts not enough? Why do we have to force a reboot? Attached are relevant logs.

[lobaro-theo]

Which version of the nrf_modem library are you using/compiling with? (See https://github.com/nrfconnect/sdk-nrfxlib/blob/main/nrf_modem/doc/CHANGELOG.rst). I believe the versions are aligned with the nRF SDK version numbers.

I am experiencing maybe similar problems with a very simple test program (performing ping and DNS in an endless loop with a few seconds’ delay in between) using the nrf_modem library versions 2.6.1 and 2.7.0. I tested with the nRF9160 (MFW 1.3.6) and nRF9161 (MFW 2.0.1). The nRF can enter a state, after a cell change, where it can send data, reports CEREG=5 and CSCON=1, but no data is delivered to the receiving socket or getAddressInfo; both simply timeout. This repeats indefinitely, with no chance of recovery other than switching to flight mode or performing similar hard resets.

After downgrading the nrf_modem library to 2.5.0, the issues seem to have disappeared. Can you confirm this as well? Which version are you using?

[Matias Marti]

Hello lobaro-theo ,

We have not used v2.5.0, only 2.3.0 and now 2.6.0. Thank you for sharing your findings on v2.5.0. My guess is that there might have been new config values that have been added to 2.6.0 that are discarded by 2.5.0 (that is, if you prj.conf looks the same).

[lobaro-theo]

I opened a new private ticket. But before I discovered that there is no dependency for this problem to the nrf_modem. It does not matter.