Please download troubleshoot package from your device and send it to me via private message. Troubleshoot package can be downloaded from "System -> Administration -> Troubleshoot" menu.
Also, what operator SIM card are you using? To what operator it is allowed to connect?
Have to connected both LTE antennas to your router?
What other modem are you referring to? Could you indicate its exact model?
Do you have any other SIM provider's SIM card, which you could try to use in this RUT9 router?