Did this ever get a resolution? we're still having this problem with our RUT955s. we have about 20 of them deployed and have frequent lockups. Our SIM management portal shows them as online but with no data being sent/received when they get into this locked up state. Theyre unresponsive by SSH or the web interface, but interestingly i can ping them from their WAN address.
We're on a private APN with static IP addresses, not sure if that makes a difference, never had any problems with the APN with other modem manufacturers. RMS is turned off. Periodic reboot is turned on for nightly reboots, but looking at the logs on the modems it seems that once it enters this locked up state, even the reboots aren't triggered. Sounds like it's something to do with the RUT software, not the cellular module side.
Thanks!