Let's try reflashing the modem then.
1. Download this: https://kaunas.teltonika.lt:444/f/0b83d2356085413a9b94/?dl=1
2. Extract those files in that zip into folder called: EG06ELAR04A04M4G
3. Upload that folder into /tmp directory of your device using SCP / WinSCP app with SCP protocol
4. Go to CLI of your RUTX12
5. Input these two commands:
echo 1 > /sys/class/gpio/modem_reset/value
echo 1 > /sys/class/gpio/modem2_reset/value
6. After that enable modem1 with command:
echo 0 > /sys/class/gpio/modem_reset/value
7. Type in /usr/sbin/quectelFlasher -f /tmp/EG06ELAR04A04M4G
8. Flashing should start, wait for it to finish.
9. When it's finished execute:
echo 0 > /sys/class/gpio/modem_reset/value
echo 0 > /sys/class/gpio/modem2_reset/value
9. Restart your router.
EB.