My e-mail provider does this. I wanted to change my password to some 64 character long generated string. It accepted, but I could not log in after that. After a few tries, I found the reason and, after another few tries, also the limit at which it gets truncated: 16 characters! God, how I hate them for this...

[–] [email protected] 2 points 2 days ago

Perhaps even worse than this is when the hash allows you to enter what you think is your full password, but as long as the first characters are a match then it will succeed.
16 characters is probably fine as far as passwords go, but if the site is secretly truncating from 16 down to, say, 7 and still allows you to sign in, you don't even realize that your password isn't nearly as secure as you thought it was.