I use a password manager with a random password generator. It's always disconcerting when I find a website that finds my passwords to be too complicated. Like "you can't use more than eight characters and the only special characters you can use are @ and !". What the shit?!?
Typically, the account creation will fail without saying why.
Is it because the site is broken? Because I already have an account? Because I used too weird a password? (10 minutes later) ok, it's because it's coded by idiots and it can't handle a 24 character password but a 12 character one works.
I once experienced a site just silently truncating a password that was too long. Such a ridiculous thing to do. It was several years ago, gaming related. I think it might have been Ubisoft, but I'm not sure that I'm remembering that correctly.
I only remember that happening once, but it wasn't some random super small site, it was Uplay. I think the limit was 14 characters, or maybe 16 I'm not quite sure, but either way it was utterly stupid.
Yeah! Why can't I use a base64 representation of a pirated 4k TS copy of Jon Favreau's "Chef" as my password? /s
Jokes aside, I've heard some hashing algorithms have a high cap of like 20 characters, so developers are probably just too lazy to switch them out or to read the docs on how to properly use said algorithms. Either way it's a very bad sign, maybe just a tad better than them emailing you the password in cleartext.
The worst I have seen recently is one with an eight character limit and support for only four specific special characters. I didn't test if it was cap sensitive but it wouldn't shock me if it was not. It is the invoicing portal for one of my clients. I wish that was the only technical atrocity committed by that abomination...it is not.