I would advise you to update from the terminal with `sudo pacman -Syu` and reboot or even better flash it with the latest image and set the APN again.
It seems that the phone either loses the communication with the modem or with the SIM, it may be software related or something wrong with the hardware.
It seems that the phone either loses the communication with the modem or with the SIM, it may be software related or something wrong with the hardware.