Looks like an issue, of the widget.
Image URLs hare handled differently for hybrid apps. And should be corrected for in the widget.
Sample to correct the URLs: https://github.com/mendix/widgets-resources/blob/master/packages-web/carousel/src/UrlHelper.ts
You can open PR to the widget here https://github.com/mendixlabs/LoginForm
What about using the core authentication widgets ?