Tom Ewer, writing at wpmudev:

Some users trying to access their WordPress admin panel have found that Google Chrome seemingly auto-fills their password. Hooray for technology! But once they click submit, they get a message along these lines:

ERROR: The password field is empty.

[…]

Robbert explains that the error stems from the fact that WordPress’s native code interferes with Chrome’s function to fill in your password.

At the linked Stack Exchange piece, Robbert had this to say:

The JavaScript function wp_attempt_focus is causing this issue.

[…]

Sadly, the function has been hardcoded in wp-login.php in lines 913-930 (WordPress 4.0).

It’s a testimony to the tastelessness of WordPress that auto-fill from Google Chrome doesn’t work on login. I’ve been working around this bug for years, and it remains an ongoing problem.