[moolight0551]

Everything seems fine with your Cumulus configuration (change logs roll over to 9am, as it is what is used in AU)

I have misunderstood your first post about this matter, and I thought that Cumulus has never done a connection.
If Cumulus lost connection after some time, and your RX units is still running, then there is a problem in USB communication.
This may seems strange but try to change the Arduino COM port from COM3 to any other available. If it don't solve, if possible check if this lost of connection still happens with another computer?

Just for curiosity, what is the USB chipset used by your Arduino? FTDI or the new chinese one CH340?

It is the Chinese CH340. I will have a look at device manager next time it happens and see if the COM port looks OK.