It could be that something else in the house is causing a lot of interference on the electrical lines. If the connection is intermittent you might try and figure out if there is a certain device that is running when the connection drops. I have a very limited understanding of powerline networking however, I think it uses frequency ranges on the power line that aren't supposed to be touched by normal AC power. I don't think these frequencies are regulated though, so your new washer or microwave might interfere with the frequency range that the adapter wants to use. At this point it looks like it'll be a lot of trial and error to figure out why the connection is so intermittent.