When Did “Not A Problem” Become a Substitute for “You’re Welcome”?

It happened again.

I got the "Not a problem" response when I thanked a cashier.

"Not a problem" to me makes what I just thanked that person for seem like it might have been "Almost a Problem."

What happened to a simple "You're welcome" or even a hit back of "Thank YOU"?

Three times in the last several days, I've received the "Not a problem" response. Each time I was thanking a cashier at the completion of a transaction. One location was  restaurant, another a hardware store, and the last a convenience store.

Each time I heard it was from a young woman - probably still in her teens or early 20s.

If this a generational thing?

Are retail transactions occasionally a problem? ("It's not a problem - this time...")

If you're every been to Chik-Fil-A, you know workers there are trained to follow up all "Thank yous" with "My Pleasures." Where the heck did "Not a problem" come from?

Is it just me, or have you noticed this too?

Thank you!