I'm a RootAdmin user. Why can't I access a specific application?

It's well known that Qlik Sense Servers can have custom Security Rules. Your environment probably has one or more rules that are blocking you the read functionality.

For example: if you disable the default "Stream" security rule, you will only see your own apps on the native Qlik Sense Hub. On the otherhand, inside NewHub you'll see all the apps that your stream can see, even though you'll not be able to open it properly.