I experienced similar PW issue yesterday even though I had established (or so I thought) a PW that used the 1st 4 numbers of my old pin. Luckily, it was a day before my next flight so I didn't experience major disruption except for the 1-1/2 hours of phone roulette to deal with this situation.

Blaming the OP here is way off base IMO. Delta still uses the pin login for website and if that's the case you honestly don't know it won't work for the phone system until you try calling.

Even with an "acceptable" PW (Anybody try a capital letter for the 1st 4 characters yet?), it's still quite confusing and often difficult to figure out letters on a phone dial pad in the heat of battle. Many softphones no longer have the letter association with the numbers so in that case it can be a terribly stressful and upsetting situation.

Even today, I notice my computer still wants to login with the old pin - even after clearing that PW (or so I thought) in Firefox prefs?

I could give them more of a pass if the website was actually an improvement but I don't see it and I'm not the only one. IMO Delta's website and apps have taken huge steps backwards and merely continue to frustrate and confuse pax.