I’ve experienced something similar with ebay and paypal, 100%.

Suddenly and out of nowhere I couldn’t login to either and had to do “forget my password” for both of them.

This triggered a several month long incident of my old passwords allowing me to log in and my new password working some of the time. I have absolutely no explanation of it but it got the to the point of having the small number of passwords I’ve used for both of them written down next to my computer. I could type in the same password three days in a row and it worked, and then the fourth day it stopped working and the another old one worked.

Deeply frustrating and still no explanation for it.