This happened to a coworker of mine. He was having sporadic wifi trouble, always in the evening but not every evening. Plugging in wired would always solve it,

This happened to a coworker of mine. He was having sporadic wifi trouble, always in the evening but not every evening. Plugging in wired would always solve it, so it was definitely a wireless problem. I handed him one of my old Ubiquiti M-series APs, the ones with the spectrum analyzer function built in. Showed him how to use it on his laptop, how to turn in a circle and estimate the azimuth of the source, etc. He went home that evening and as soon as his connection dropped, he fired up the analyzer. Very quickly localized the source to the driveway side of the house.... to the neighbor's kitchen. At that point he called me for advice, and I said to knock on the neighbor's door, because this is really unsafe. He put me on speakerphone and I was able to tell them what we found, and they cut me off, saying they knew the door seal was damaged -- it got torn a few weeks prior when someone caught something in the door -- they just had no idea it was a big deal. (It's normal to feel a warm draft near the corner of the unit since the fan exhaust blows out down there, so the warm-sunshine feeling wasn't distinct enough to alarm anyone.) They replaced the microwave the next day and the problem went away.