Have you thought about opening an application directly using the url? In addition, if you are trying to create a guided app that doesn't allow going back out to the hub you can add a css reference to the hub.html that will contain code to hide the toolbar.
The css reference is
There is something I don't understand. From what you say, I understand that the user is redirected to Qlik Sense from the ERP but apparently there is no security there if they can navigate to the hub and see others apps and you don't want them to be able to do such thing.
Are you using the same QS user for many ERP users and many QS apps and that's why you have the problem with the "go to hub" button and the app visibility?
Because if you are using a different QS user for any different ERP user, you should be able to manage the security using security rules and the users wouldn't see any Stream or App they shouldn't see.