I just found out yesterday night that plugging my Apple branded Macbook Pro's AC Adapter into an electrical multioutlet caused the nearby powerline adapter to stop working completely.
While it is certainly true that the powerline installation guide recommends to NOT plug the adapters into multioutlets, it must be said that until yesterday it was working just fine in that way.
Removing Mac's AC adapter restored the operations immediately.
So, if you are wondering why your powerline has suddenly stopped working, you might consider if you have plugged some new electrical device somewhere.
I don't know if the problem is just in the proximity of the devices considering that the AC adapter is normally plugged elsewhere and it doesn't seem to interfere with the powerline or if it needs to be placed "on the same wire", let's say, in order to break the signal.
At any rate, this is what I experienced.