After visiting broken routers:
> router shows "DISCONECTED" state but show LTE Network
> there were no information about received sms with reboot or status (there was no requested reboots in logs also),
> last sms was from 1st May - before router failure,
> local reboot did not solve the problem,
> update from 6.05.3 to 6.06.1 did not solve the problem,
> downgrade firmware to 6.0.4 did not solve the problem,
> uploaded Restore Point with proper working configuration also did not solve the problem,
> factory reset - did not solve the problem,
> Mobile operator claims that SIM card is active with proper IP (static IP in APN),
> Configuration for public/operator APN did not solve the problem.
Router will be exchanged but the big question is why operator see SIM card as active.
If router was dead, the operator should see SIM card as not-active.
Why that situation happened in two routers from the same series.
Both routers are located with 4 km distance between each other.
Both routers are in the neighbourhood of 5 BTS LTE.
Both router were updated with big fv jump:
3.832 -> 6.05.3 - that router started working after 2h after firmware update to 6.06.1
4.103 -> 6.05.3 - that router is still dead.