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 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 go to the admin page (https://[yourdomain]/admin).