F'rinstance, a few weeks ago everybody in Lafayette, Indiana apparently decided to go run out and buy 12ga 00 Buck.
Ah! Now I know who to blame
This week, it appears to be 12ga slugs. Two weeks ago, it was .308.
Up until a few weeks ago, there was a fixed and predictable demand for .380. That changed, of course. People who'd bought cute little guns and left them in the sock drawer years ago are the folks who are now digging them out and realizing they forgot to get ammo.
(Picture panicked guy in a $40,000 car, wearing an $800 suit, with a $75 Jennings, yelling, "but I need .380 shells to fill my clip! I gotta stand up to the fascists/communists/zombies when they come!" Welcome to my world.

)
Thing is, not many folks reload .380 and most folks who shoot it don't save their brass. Couple this with a low demand, and most commercial reloaders were just melting it down. Unlike other calibers, there just isn't a reservoir of spare .380 brass laying around, and the ammo companies are having to scramble to produce it.
My understanding is that the commercial companies are ramping up slowly, because they expect demand to plummet at any point now. Nobody wants to be sitting on 30,000 rounds of .380 in the stock room come April.
The good news is, this will pass. Most folks just want enough ammo to fill the gun they've got at home, and when that demand is satisfied, I forsee .380 being readily available.
...then there'll be a run on something else we don't expect. Like .475 Linebaugh.