Spitz AX (GL-X3000NR) SIM registration issue

I'm using the Spitz AX (GL-X3000NR) in the UK with an EE SIM and have a strange issue to report. Initially when I set the SIM up, the only connection was LTE FDD (4G+). I had tried using the IMEI of a spare phone but the connection wasn't able to achieve a NR5G-NSA connection.

I then tried using a Vodafone SIM in slot 2 to evaluate speed and decided to stick with my EE SIM as it is several times quicker in my area. This is where my issues started. Changing back to the EE SIM, the Spitz could no longer connect using the EE SIM, it would always say "SIM card not registered" - even though the SIM worked fine in a phone. Performing a factory reset also did not work. I also re-flashed the firmware, but I think that also did "nothing" that a factory reset wouldn't have already done.

What eventually worked (although maybe it is coincidental and a timing related issue with the local towers by using the EE and Vodafone SIMs using the same IMEI?) was running these commands, I can't remember the exact order:

AT+CFUN=1,1
AT+CFUN=0
AT+CFUN=1

Upon a reboot, my EE SIM could connect once more, but rather than connecting with only LTE FDD, it is connecting with NR5G-NSA, great!

What would cause the above behaviours? Do the above commands do anything that a reboot or factory reset would not accomplish?

Spitz firmware: 0408release4 (2024-04-19)
Quectel firmware: RM520NGLAAR03A03M4G_01.201.01.201 (2024-03-28)

hello
When did you upgrade the Quectel firmware?

I upgraded the Quectel firmware a little while after taking delivery of the Spitz AX, so I think late April. I upgraded the modem firmware as my EE sim was connecting to 4G only and I'd read on forums that users on other networks managed to get 5G connections working with newer firmware. In my case, updating the firmware did not change the connection until the issue I had with the Vodafone SIM mentioned above, and eventually running AT+CFUN commands and rebooting.

Resetting and refreshing the firmware is equivalent to executing CFUN=0/1
The problem may be caused by imei