The worst one is when it only supports up to like 16 characters but doesn't tell you so it will only use the first 16 characters and ignore the rest. The next time you need to enter it and get the 64 character password from your password manager it will just say it incorrect and you're left with no idea on why it's wrong.
To order through their site, I try to use the places own sites instead of justeat etc so they get more of the money. As you can imagine they aren't the best websites though.
Sometimes there's a limit on the length but it's only imposed by the JavaScript of the website, so I can use my password manager to insert the text directly into the field but I can't actually type it in.