“no prob”. Ugh. The latest substitute for the reply “You’re welcome!” It’s why I refuse to say “Thank you” anymore to anyone in commerce. Nine times out of ten I’m going to get the dreaded NP back instead of YW. I mean if I said I was sorry I stepped on your tail or something, then I could understand “no problem” as a reply. But NOT as a reply to “Thank you”. Where do they teach the kids this stuff anyway, in high school?
It might come as a surprise to you but use of expressions and language generally does change over time. Perfectly competent users of English antedating you by a century or two or three might have some serious issues with your own usages.
no prob seems to be a problem for you. To many others it is no prob