Hi Keith,
A power supply may indeed be the source of the issue in your case. On the Reach M2 JST-GH or USB port, the voltage should be in the range of 4.75 - 5.5V. Please also note that the RFD can consume up to 800mA in peak, so make sure that your power source can provide enough power for both the Reach and the RFD900. Can you connect only RFD900x radio, without LoRa, and let me know if it works?
Can you also explain your desired workflow? Emlid Flow only supports 1 correction output/input option at a time. Why do you want to work with 2 radios at the same time?