Yes, I remember flailing about at a repair station on a prior floor. I believe it was materials three, right after coming out of storage. During storage, I'd acquired a hoard of pristine bipedal allies all at once. I was perpetually suspicious of the game's generosity, so I tried to get most of them killed off before they "betrayed" me, but a couple of them made it out of the branch, one missing a weapon. At that point, I figured I might as well keep them around, but I couldn't figure out what the unarmed one would be useful for other than decoy duty. But before I could apply him to that, I stumbled across a repair station. I'd always seen the "refit" option available there, but I never knew what it did; I'm still very new to the game. My best guess was that it was used to repair allied robots, so I hit the command a bunch of times. I ended up getting locked out (I really wanted to restore my ally), but I got some notification about this "backup laser 1: thing and a ~30 second timer. Knowing I would probably die if I stayed, I ran off, and that was the last of the matter I heard of. My allies died shortly afterwards.
At no point do I remember possessing or interacting with the weapon. I never equipped it, and it never showed up in my inventory. I never noticed it taking damage.
I don't know what a mechanic is or how one might have "given" it to me, but if the repair station didn't, perhaps that could have been the source.
However, there is a point which I think may have caused the peculiarity. In storage, I stumbled across a beautiful pristine prototype guided EMP launcher weapon which I carried around with me until just recently in the save file, when I botched the repair hack (Detailed in my last post). I still had this, and only this, equipped for the floor after storage and the first floor of factory. At least, that's what I recall. Now, I don't know exactly what refit does, but if it "gives" me this item by directly equipping it to my weapon slot, then perhaps it didn't recognize that the EMP launcher took up two slots? That could cause a conflict, if the repair station saw that I had only one weapon equipped but I had two available slots, without recognizing that the weapon was two slots "wide".
That would also explain why this hasn't come up before, since most people would consciously realize that a refit would be useless without an open slot. I didn't know what refits did (I still don't really), so I didn't make the connection that it would be a waste of a hack. Multi-slot weapons also seem quite rare, which would also cause it not to have come up (The EMP launcher was the only one I've ever seen, and that was a prototype on a branch).