Mine has persisted across a reboot as I recall but I will reboot and see what it does.
You guys are correct... it's not persisting across a reboot and reverts to GSM/WCDMA/LTE Auto.
I rebooted 3 times to be sure.
Now we know.
I also made a video describing the procedure.
(Only making vids because someone told me that I have a lot to offer in the realm of electronics work.. but I am retired from that
It's here if interested...