Night Hawk R6700 app update issue

Have had this router for over a year and loved it and how I could control device access to our WiFi through the accompanying app. This was the main reason I purchased the router and when I went to turn off my son’s WiFi access yesterday I was prompted to update the app. Now the app doesn’t register any recognition of the devices that are still operating on our WiFi. Router is still working but I now have no control over access. Anyone who can help?