- Having confusing language and poor differentiation between the sign in and sign up form. Symptom, users start filling in the wrong form only to realize their mistake.
- Separating the password from the email field with an extra mouse click sucks if you are using a password manager. Doubly so on mobile where using password managers involve a bit of fiddly interactions. Having to do this twice sucks. If you do this, at least have one of the fields in the dom tree but hidden so that it gets filled with one click via your password manager.
- Not making the login form password manager friendly my not sticking to conventions for field names for this.