Error occurs on form attribues in chrome.
This issue occurs on Chrome if a form field fails validation, but due to the respective invalid control not being focusable the browser's attempt to display the message "Please fill out this field" next to it fails as well.
A form control may not be focusable at the time validation is triggered for several reasons.
This fixes the error
$form['#attributes']['novalidate'] = 'novalidate';
This causes no risk because this is pure client-side behaviour.