Have you tried with a different ethernet cable in case the current one is faulty?
Is the fetch the only thing plugged into the powerline adapter?
Are the powerline adapters plugged into wall sockets or power boards?
I'm assuming the different wall plugs you tried were all in the same room.
I have a powerline adapter that really sucks when its plugged into my preferred spot in my room, but works significantly better when plugged into another rooms wall socket via power extension cord. While not an actual solution, it at least identified the electrical wiring as the problem. Maybe you can do similar tests.
Shouldn't be an electrical fault as it only started doing this last week.
I'm not saying its an electrical fault as such, just that the electrical wiring may not be as suitable for data as it once was.
Prior to this only ever had one problem which was the powerline adapter hence the reason that I bought new ones.
And the powerline adapter sends the data over the home electrical wiring. So it could still be the wiring, especially since you said there was no change after replacing the powerline adapter.
I'm only suggesting that if you have a power extension cord that you could do some testing using the power extension cord in different rooms.
As in.... Use the extension cord in a different outlet and plug the adaptor into the extension cord?
Hope it's not the wiring as the house is only 5 years young
Remember that your home electrical wiring is not designed to handle data as well as electricity, so if the powerline adapter does not work well it does not mean that you have faulty electrical wiring.