The login page may require a user to reset their password every time they log in. This issue is typically caused by a bookmark or link that contains extra information in the URL (in the form of a query string). This information instructs the site that the user's password is incorrect or needs to be reset. This can be caused by copying the link from a Password Reset or Account Validation emails.
Please update any bookmarks that direct to the site to use the homepage (https://[yourdomain]) and click the Sign In button or to the admin page (https://[yourdomain]/admin).