The control panel and rfx firmware are almost always a matched set. if you are trying to do 2 way on rfx and are using both ports 3 and 4, that may be your issue. Ports 3 and 4 share a single UART. Only do 2 way on ports 1 and 2. if you MUST do 2-way on port 3 or 4, make sure you use only ONE of the ports. This means you have only 3 useable 2-way ports and that you should avoid connecting equipment to the last unused port.

A search for shared UART will likely provide more info.