@David-TP 

Yes, you are correct in thinking the reason for upgrading is a think wall. I live in an old stone house with an extension wrapped around it. The result is having one thick stone wall separating the rear of the house from the front.

I've not noticed any red light show on the px50 when they drop out occur, however next time it happens, I'll make sure to check all of the satellites.

The app shows all connected PX50 units are on the powerline backhaul.

I've also swapped the main unit with a different one, thinking I maybe had a faulty satellite. This didn't help in rectifying the issue. 
 

I can't confirm this yet but it seems to be effecting IOS devices. I'll do some more investigating and get back with confirmation on that though. 
 

James

Just an update,

My android tv, which has a wired connection to one of the satellites also suffers from the drop outs, so not necessarily just an IOS problem.