Here are three noteworthy examples for you:
(1) my late Dad’s Cadillac: (1999 model) .The driver’s side rear mirror is a photo darkening type-it goes dark at night, so you are not dazzled by rear headlights. A year ago, it had changed color and was all fogged up-I thought it had become broken.In the last 6 months, it has cleared up and works fine!
(2) My mother’s microwave oven (at her beach hose). When I opened the house last May, the microwave oven was dead-no display, no reaction when I pressed the buttons. I left it plugged in-a month later, it came back to life!
(3) I had a quartz watch that the battery had died in. I put a new battery in-and it would not run (curiously, the chronograph feature/timer worked). I was about to junk it-till I checked it-it now runs perfectly!
Is this unusual? Is it an example of corroded electrical contacts becoming conductive?
For this one, at least, there might be an explanation. I had a similar thing happen to my microwave a couple months ago. The display lit up, but the buttons didn’t react. A quick unplug/plug in again did nothing.
I checked around on the web, and one page said to leave it unplugged for 5 minutes, then plug it in again. That did the trick - it started working again, and has worked fine ever since.
Is it possible that maybe you had a power outage that effectively left the microwave off for a while?
My car has this light-up display thingy that can show you date, time, direction, gas mileage, etc. Following a rear-ender, it quit lighting up except when the interior lights were on. Recently my sister came to visit. Whenever she was in the car, the thing would light up. She’s gone, and it no longer works.
The digital clock on our stove started blinking one day then went out. We had a power outage a few months later and the display came back on with the power!
I have a cheap didgital clock in my car - got in one day and the thing was completely black. Later on, I noticed it was back to light grey with the black lettering showing the correct time.
Odd.
That happened several times.
It was a couple of weeks later when the kid worked out that when I parked in a sunny spot, the car would heat up to the point where the liquid crystals would expand and cover the whole display field, as the AC kicked in and the car cooled down, everything shrank back into place.
It’s quite entertaining to watch the thing drawing the inky blackness back into itself, like some ‘cursed evil’ effect running in reverse.
I gave my first wife a valentine’s gift - it was a singing bear that sang with an Elvis “tone” “Hunka hunka burnin’ love, wwaaahhhhhh!”
I found it years later, after she left me. It was in the basement. It didn’t work, no matter how hard I tried to make it work. Me and the new GF were having a bonfire and we threw it in. The damn thing started singing! I attributed it to demons. 
Oh Uber! I am giggling over the mental picture of the burning bear singing, “Hunka hunka burnin’ love, wwaaahhhhhh!” from the depths of the raging fire. So funny!
I took my little Netbook on a 10 day trip to Europe but never used it. As soon as I got home I turned it on but the screen was screwed - all wavy lines and messed up - but when I jiggled it on the hinges it would clear up. Eventually it stopped clearing up, no matter what I did. I chalked it up to a) the chew-mark up in the corner from when my dog chewed on it and cracked the screen + b) being jostled around my backpack for 10 days. No big deal, I plugged it into my husband’s old monitor and carried on. One day I glanced at the screen…and it was fine. No wavy lines, no messed-up-ness, FINE. It sits on the table and I don’t move it around. My husband used it downstairs when fixing his TV and it buggered up again, but after leaving it alone for a while it’s again fine. Weird.
I wish a third person was there to get the looks on our faces on video… :eek:
This morning, the old Caddilac’s RPM display started working again-after not working for 4 years! I think the old car likes me!
I have a stopwatch like that. I once washed and dried it on hot (I left it in a pocket). It was OK 10 minutes later.
I used to have a 4-channel mini recording studio. It used cassette tapes. After years of use, one day track 4 either didn’t record or didn’t play back. It did, but with little volume and somewhat distorted. I tried all sorts of stuff, then figured the thing was hosed. My father asked me to pack it up and send to him, as he had tools to test it with. He said he couldn’t find anything wrong with it. When he sent it back, it worked.
Son’s iPod nano
Went through the clothes washer
Dried it out for 24 hours before charging or turning it on.
Works perfectly 