XAV5001, XAV5221 XAV 5421 all compatible? I am having random network issues.

Thanks in advance for any help this is driving me up the wall!

I had two XAV5001s connected fine in my property to connect my broadband router to an Apple Time Machine acting as an Airport Express wifi router. My house is large with thick stone walls so the broadband router provided an East network and the Airport Express a West network, connected in 'bridge mode' so the broadband router acted the overall DHCP server.

This worked fine; wireless clients such as iPhone, Macbooks and iPads could connect and see devices from either network, and has worked for about a year.

I needed to connect in a NAS and a Naim Mu-So remote speaker, and another AIrport express for remote speakers again, so purchased the 5221 and 5421 pairs to extend my powerline network. I checked the Netgear site and they seemed to be compatible but....

I connected the Time Machine to the 5421, which is a passthrough powerline adapter so that I could save a power socket, and since it introduction, for some reason I randomly can't get clients that connect to the West network through the Time Machine to see the internet. They seem to have aquired IP addresses and know their DNS server, but via the Airport express they get no external connectivity. The NAS and the Mu-so work fine via either 5221 or 5421 adapters and can stream from the internet, but the Time Machine/Airport express can't connect through for some reason. Yet the LEDs on all devices are red showing there is (poor) connectivity, even when the Time Machine access is blocked.

I have downloaded the Mac utility and use the sudo procedure I found on a support website to launch PLC under El Capitain on my iMac. It scans the network and can find the adapters although the 5221 and 5421 come up as 'un named'.

So - for example, yesterday during the day I was able to connect to the West network and surf the net and get emails on wireless devices. In the evening some time that all disapperared and devices connected to the West network could no longer access the internet, even through the LEDs on the powerline adapter connected to the Time Machine were green or red (but not extinguished) and the LED on the front of the Time Machine was green indicating that it didn't think it was down. I power cycled the 5421 (and Time Machine as well of course) but still no Internet connectivity. Yet at the same time, connecting to the East network from the other side of the house worked fine i.e. directly to the wireless network servered from the broadband router.

Help.....!