Hi, I have a virgin router and 4x deco p9.

1 is the main unit connected to the router. 
2 are connected using Wi-Fi and power line

1 is hardwired via a hub.

all have been working fine for 9 months with no issues at all. Then 2 weeks ago one of the units connected via Wi-Fi and power line started dropping the internet off. Can do it 5 times a night and seems to need resetting to connect again. I had a spare p9 so tried swapping it and that's exactly the same.

what could be causing the one unit to suddenly start dropping out? 
 

any recommendations?

thanks