Powerline adapter stopped working on a certain set of outlets

I had used my powerline adapter on a certain outlet for a couple years, but at one point that outlet (and one nearby it) completely stopped functioning with any powerline adapter. Both outlets still work properly for normal use. 

What could be the cause for this and how do I fix it? 

I have since found a new working outlet to use it on, but in that outlet the internet is knocked out whenever the microwave is in use. I cannot find a solution to that either.