Ok, I have tested and retested and all of my colleges have the same issue.
1. Create a report with 1 visible and 1 hidden tab
2. On report 1 either use a drill through or a button/image to "navigate" to a bookmark on the hidden tab
3. Publish to PBI Service and create an App using the "New Navigation"
4. Go to the app, click on the button/drill through to navigation from the visible page to the hidden page
5. Now in the new navigation, click on the visible report name
6. Happy "Almost Done" endless loop.
It seems to have an issue when navigating from hidden tabs.
The problem is, I might have some drillthroughs that dont make sense unless you make a prior filter selection so I want to keep them hidden. But if the user then tries to return to the "home page" (aka visible report) they are buggered!