NetScanner for iPhone, iPad and Mac. If you have questions, find a bug or have a wish, write to app.sascha@icloud.com. Please include the device, the iOS or macOS version and the app version (shown in the app’s About screen).
You can find the privacy policy and the legal notice here. (German version: Support.)
The app needs the “Local Network” permission. Without it, the system drops requests to devices in your home network. Check under Settings → Privacy & Security → Local Network whether NetScanner is enabled. The device must also be on the same Wi-Fi as the devices you are looking for.
iPhones, iPads and many other devices use a random (“private”) Wi-Fi address. There is no manufacturer information for it. If a device reports a name or model otherwise (for example via Bonjour), the app uses that to guess. iOS does not release the MAC addresses of other devices to apps; the app gets them from Bonjour, UPnP, NetBIOS or the router’s device list.
Only so that the system releases the name and signal quality of the Wi-Fi. The app does not read any location coordinates and does not store or transmit a location.
The speed test uses the open measurement service of Measurement Lab (M-Lab). Depending on your connection, the app transfers several hundred megabytes; on mobile data this can use up your data volume. M-Lab publishes the measurement results including the IP address as open data. The test only starts when you tap “Start”.
It is optional and meant for FRITZ!Box routers. You enter the address, username and password. The app uses them to read the device list directly from your box. The password is stored in your device’s keychain and only sent to your own router. Access for applications (TR-064) must be allowed on the box.
Please tell us what you did just before the crash. The crash report helps: Settings → Privacy & Security → Analytics & Improvements → Analytics Data, entry “NetScanner”.