The app banner is not showing when tool_mobile | enablesmartappbanners is set to Yes.
- App banners for iOS devices (iPhone, iPad or iPod) are only shown when accessing the site using the Safari browser
- App banners for Android devices are only shown in very recent Chrome browser versions and when the app is not installed. Note also that Chrome uses an engagement heuristic that will display the banner only on certain conditions, like interactions with the site, the last time you interacted with it, etc. You can remove the engagement restriction check by disabling this special chrome flag: chrome://flags/#bypass-app-banner-engagement-checks
This was tested by using an Android device without the app installed in a recent chrome version.
Where does this banner normally appear as I think it may be our theme that is causing this to not appear.