ESM Error Code 50: type ipv4 only allowed (NRF91 Asset Tracker)

[Dominic]

Hi 

I am a bit stuck on this one. 

Hardware: NRF91 Thingy, NRF91 DK

Firmware: Asset Tracker with latest MFW v1.3.5

I have been connecting with 1oT SIM using NRF91Thingy and DK perfectly for the last 4 months - and it is usually the O2 cell tower (LTE-M Roaming) as there is no other tower nearby. I left it attached and logging on October 22nd 2023 and a few hours later disconnected, I have not been able to connect since. Every time I connect, or use AT+COPS it attaches then immediately detached with ESM 50 code - (PDN type IPv4 only allowed). I have contacted 1oT and they haven't reported anything with O2 network.

Modem trace as follows:

%CESQ: 32,1,16,2
+CEREG: 2,"02D0","07F87C78",7
+CSCON: 1
%CESQ: 33,1,9,1
%CESQ: 33,1,14,2
[00:00:01.534,149] <inf> app_event_manager: DATA_EVT_CONFIG_INIT
[00:00:01.935,821] <inf> app_event_manager: MODEM_EVT_LTE_CELL_UPDATE
+CGEV: ME PDN ACT 0,0
+CNEC_ESM: 50,0              <------- Error Code
%MDMEV: SEARCH STATUS 2
+CEREG: 5,"02D0","07F87C78",7,,,"11100000","11100000"
+CGEV: NW DETACH             <------- Detach
+CGEV: ME PDN DEACT 0
+CEREG: 2
%CESQ: 35,1,19,2

I have never seen this issue before and nothing has changed in the firmware since I started logging started. 1oT assume its hardware/firmware related - and suggested I changed the PDN context to use IPv4 only, same result. I also switched to IPv6, it gives a EMM 15 error in that case. We can connect to Vodafone just fine, but it is quite low signal, either way O2 has always been the closest and the best to connect to. 

Has anyone had similar issues? 

[Dominic]

an update to this, I have Wireshark installed and I am now reviewing the modem traces. I had it all wrong, it's not the network detaching the NRF91, but the NRF91 is requesting a detach!

NAS EPS session management messages: Activate default EPS bearer context request (0xc1)

NAS EPS session management messages: Activate default EPS bearer context accept (0xc2)

DLInformationTransfer, Ciphered message  <<---- Not sure what this is

NAS EPS Mobility Management Message Type: Detach request (0x45)

NAS EPS Mobility Management Message Type: Detach accept (0x46)

Cause: No Suitable Cells In tracking area (15)

Duration about 1second! 

So NRF91 is detaching for some reason, I don't know if that ciphered message has anything to do with it, for some reason it doesn't think that cell is suitable anymore. I need to dig more to why, 

Thanks for anyone following...