Last night all rf nodw data stopped arriiving at the controller again.
This time I simply power cycled the arduino gw and 50% of nodes started to display data again.
After half an hour this was still the case so I stopped and then started again MYC (no power off on the pi at all). Suddenly the remaining nodes started to show and this morning it's still looking good.
I'm still struggling with why this happens, especially as this would indicate it is neither the gw arduino or controller pi that is solely responsible.