I came here looking for a solution to this exact problem.  We recently installed the P7 in a large multi-story home.  The powerline backhaul was what was attractive as placing more units all over the place to cover every corner wasn't cost-effective (or a good solution).

Like @MarcH we are seeing the exact same issues.  200Mbps internet into the home, yet we find that the home's security cameras were constantly going offline and usage was overall sluggish at times.

 After a little more troubleshooting, we were finding VERY SLOW speeds over WIFI, and that the Deco app was showing my device was connected to a Deco whose source was another Deco with one bar.  

Two story home, with main Deco downstairs at one end, another Deco downstairs mid-house, and another Deco upstairs at the other end of the house (furthest from the main Deco).  Yet the upstairs Deco would show it's source as the downstairs Deco at the far end, not the Deco mid-house, which is closer.  

Regardless, further testing with wireless AND wired clients (wired into the Deco's ethernet port) showed SLOW speeds.  

Today, I was noticing that while the Deco's plug has a green light, one of the Deco's LED change from green to flashing red and stop communicating.  Yet the Powerline indicator was green.  

Given everything I have tried and tested, I find no proof that these P7 Deco's use the powerline at all.  They all seem to communicate over Mesh, which goes completely against what the P7 was made for!  Advertised for multi-story homes to use AC wiring so you don't have to place AP's all over the place.  

There is obviously some sort of bug in the P7.  Is anyone looking into why the P7's powerline fails to be used?

Any news on the update to the app?

@MarcH 

Hi,

I have had a word with a lot of network integrators and i have finally come to a conclusion that powerline technology is a waste of time and money with the complex wiring we all have at our homes to even bother on. I have installed multiple Decos in my 4 storied bunglow and it works like a charm. Its better to have multiple decos and try the main deco to be in the centre of the whole configuration. If you require any help just let me know i will explain you things in much detail.

Shashank Khemka