Hello!
After update firmware in my both RC one of them (primary) not connect to DJI GO app. When I insert the usb cable into the tablet (android), it only charges. DJI go 4 does not show connections to the RC. I am trying other cables and devices, that workin on slave RC, but no effect. Herewith, the remote connects to the drone and the led lights green.  How to resolve this issue ?  Before the firmware update, everything was fine!

In your situation, I would recommend you send your RC back for further check. Please contact our support and start a case: http://www.dji.com/support