When you change the image on an infocard to be displayed on the mobile version, it won't be shown. Instead, the main image stays being shown.

• Open an infocard on site-editor for editing.
• Change the main image of the infocard and apply.
• Change the image for the mobile version of the infocard and apply.
• Observe the results, the image will still be the main image instead of the one set for mobile when in mobile mode.

Instead, try to use a flex layout with a store image + other apps to create the desired banner.