Is you app published or unpublished? The help file says that this makes a difference in what is exported:
You can export apps. For example, you might want to use the app in a local version of Qlik Sense, or export the app to another Qlik Sense site. For an unpublished app, all content is exported. For a published app, only published and approved content that is part of the .qvf file is included in the export. The exported app is saved in the default download folder of your web browser.