The Autofill function requires a card to has correct autofill attributes. They are usually assigned automatically when the card is created, but you can check them by pressing the Autofill (Magic wand) icon (Desktop and Mobile versions) on the toolbar of the Edit Card window.
Make sure that the card’s fields have correct autofill attributes: User name, Password, Website (for web resources), and Application (for apps).
If on some websites you need to autofill one or several additional fields inside a login form, you can configure attributes using the autofill extra field feature. Details on configuration can be found here: https://safeincloud.ladesk.com/951468-How-to-autofill-extra-fields