What are MCC and MNC in debug messages for RG1xx-LTE?

Let's take these messages as an example.

SGSN='12085978.mmecE4.mmegiFF09.mme.epc.mnc410.mcc310.3gppnetwork.org' 

 SGSN='120631.mmec5f.mmegi8004.mme.epc.mnc260.mcc310.3gppnetwork.org', 

The physical network providers are identified by their MNC and MCC codes. The MCC is the mobile country code. In this case it’s in the US so all physical networks in the US have an MCC of 310 . In the logs when the network deletes the PDP context and hands over the cellular connection to another tower with a different provider. You can see the MNC value switch between 260 and 410 which corresponds to ATT and T-Mobile. In each case because the PDP context was also deleted by the network the handover also caused the modem to re-attach which you can see from the network log that it did. Handovers in good signal strength areas usually make sense if a device is moving.