Even though the device is not specified, Teltonika routers with 2 x SIM slots can't have them both operational at the same time. Only one can be used while the other is a failover option.
In the future Teltonika will release a router with two cellular modules, which means that both SIM cards will be able to work at the same time. It's called RUTX12 and it can be seen in our products catalog: https://teltonika-networks.com/networks-products-catalog-2020-january.pdf
However, at this point the release date has not been set yet.