Garage Gremlins: They live in the rafters or under your work bench. When you drop something, they grab it, move it to another part of your garage and leave it there for you to find days or weeks later.
I had one that used to live in my garage. I named him 'Stupid S.O.B'. Whenever I'd misplace something, a tool or a part I'd say, "Okay, what did you do with it, you stupid s.o.b ? That's how he got his name.
Garage Gremlins are great at sneaking from their hiding places and moving things around when you're not looking. They take things, hide them and put them in places that you were never near. Like on the freezer on the other side of the garage.
No, it isn't your memory or your brain cells that are dying, it's Garage Gremlins.
There is no way to get rid of them, no repellants that you can spray or poisons to put out. If you have them, they're there to stay so just deal with it. Good luck.
Tom