Hi,
Modem unreachable means device can’t connect/use modem, so all features related to modem won’t work.
If possible try updating to newest device FW and check if modem starts working.
Also if you can use CLI you could try these steps (executing lsusb and if there is value with 9008 then modem can be recovered):
https://community.teltonika.lt/t/rut950-internal-modem-is-unreachable/12787/5