Nighthawk App

Two separate things going on here, the app and the router. I'd start with the router, which is best sorted out here:

General WiFi Routers (Non-Nighthawk & Non-Orbi) - NETGEAR Communities

Fix that out the app problem might go away.

What firmware version do you have on the device?

A number is more useful than "the latest". (It may not be by the time people read this.) There can also be newer versions, or "hot fixes", that do not show up if you check for new firmware in the browser interface.

It might also help if you told people what the modem is in front of this router, if there is one. The model number could be useful. Is it, by any chance, also a router, with a set of LAN ports on the back?

The reason for asking is that a lot of people turn up here trying to put a router behind a modem that is also a router. That can complicate troubleshooting.

Apologies for all the questions. But you can help people to help you by providing the information suggested in this forum's header:

Subject (Include model number and brief summary)
Model (Recommended - Helps the community give the best answers)
Body (Include additional detail including model version, firmware, OS and environment where relevant.)

They are there for a good reason.

In the meantime you could visit the support pages:

Support | NETGEAR

Feed in your model number and check the documentation for your hardware. Look at the label on the device for the model number.

You may have done this already. I can't tell from your message.

I mention it because Netgear stopped supplying printed manuals and CD versions some years ago and people sometimes miss the downloads.