Some customers have experienced an issue with connecting to the 4G network when using an EE SIM Card directly from EE. Teltonika have already provided a fix for this so if you are experiencing an issue connecting to EE 4G network with EE SIM then you can download the firmware and update your router
here is the link
https://www.westlake.co.uk/Teltonika/RUT9XX_T_DEV_00.06.02.92_WEBUI.bin
Once you update the firmware then there will be no issue – Solved!