Hi there! I understand your Netvue app on your iPhone has suddenly stopped working, and you've already tried switching between WiFi and cellular networks with no luck. Let's work through this together to get it back up and running.

To start, could you tell me a bit more about what exactly happens when you try to open or use the app? For example, does the app load but fail to connect, or does it crash or freeze? Are there any error messages you see?

In the meantime, here are some useful troubleshooting steps we can try:

1. Check cellular data permissions for the Netvue app:
- On your iPhone, go to Settings > Cellular.
- Scroll down and make sure the toggle for Netvue is ON to allow cellular data usage.

2. Restart the app and iPhone:
- Force-close the Netvue app by swiping it up from the app switcher.
- Restart your iPhone to refresh the system.

3. Ensure app and iOS are up to date:
- Open the App Store, tap your profile icon, and check for updates for Netvue.
- Also, check your iOS version under Settings > General > Software Update.

4. Reset network settings:
- Go to Settings > General > Reset > Reset Network Settings.
- Note this will erase saved WiFi passwords, so save them somewhere first.

5. Check app’s network compatibility:
- Netvue devices usually require a 2.4 GHz WiFi network, not 5 GHz. Even though you tried cellular, the app itself might attempt to communicate via WiFi when connecting to the cameras. Confirm your WiFi is 2.4 GHz 3.

If you've tried these or have details from the app’s behavior, let me know so we can explore next steps or delve into app settings and account checks.

Are you able to share what happens when you open the app or receive error messages? That will help me guide you better.