Once I registered on a website. I used an auto generated password. Next time I tried to log in to the website I was confused that my stored password didn’t work. Requested to change the password, but I used the stored password again. To my surprise, it said the password must be different from the current one.

After a bit back and forth I finally figured it out. Apparently the site had a max length on the password. Any password longer than that is truncated. This truncation wasn’t applied in the login form. Only when creating a password.