My RUT950 running FW version RUT9XX_R_00.06.06.1 (latest as of today) had a similar problem, but was in the night after I performed the initial setup (lots of "Save" button presses) so i assumed it might not be a "full bug".
I have two SIM cards inserted, SIM1 cannot register to network, while SIM2 is functional (Vodafone also). Left the device with the (ethernet) WAN link unplugged, and after some time (probably when the provided interrupts the link to force a new IP) the device started to switch back and forth SIM2 -> SIM1 -> SIM2 -> ... for hours without being able to register with the SIM2 again, until I rebooted.
@Teltonika: I collected the logs at the time. They do not cover the start of the outage, but i see the modem manager daemon failing to recognize a registration and then the SIM switch taking over.
