The Unsolved Mystery of The Rogue Kitchen Cabinet

Hi-lo there, everyone!   Something happened in my kitchen the other day that is... baffling me.  So I thought I'd share!

So here's the basics of the background.  I have a very old house. Built before the war. I've owned it for a few years now, and we've been doing some renovations these past couple of years. It started with the foyer at the front of the house, and then we did some more work to the living room and the dining room right next to it. We did a little work on the bathroom floor, but we haven't done anything to the two bedrooms or the kitchen. No work in the kitchen, just to remind you.

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I was hanging out in my kitchen, you know, just mindin' my own, doing my thing.  Wiping off some countertops, you dig.  When suddenly, I hear a "ping" noise.  Like something is flying off into the ether.

Then, I see this.

PLEASE TO BE IGNORING MY DIRTY FLOOR.  I'll sweep it soon.

Now I know what some of you are thinking. "What on earth are you doing? Why do you have a kitchen cabinet right next to the fridge? You can't even open that cabinet!"

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I know. I know.

Which is what made it even weirder to me. That cabinet hasn't been really used or even touched in probably.... six years? So what happened? Why now? Should I be concerned about the rest of my cabinetry?! Is this something I need to consult.... professionals for?!

I tried to do some Googling, but everything I searched for tried to get me to buy another cabinet, instead of telling me WHY this might happen.   So, I turn to you, gentle reader.
Seriously, I don't know why this happened now, but NJ has already told me he's on it. I texted him about it and he said, 'I Will Fix', so.... He Will Fix. But why did this happen? What do you think was up with the mystery cabinet?

Cabinetly yours,
Behka