Hearing safety: in bad Bluetooth states the device can emit a sudden loud tone. The Nuraphone disconnects when it isn't being worn, so keep it on your head but with the in-ear tips out of your ears while connecting or changing settings, and only seat the tips once things look stable. The app refuses to connect while the headphones are connected for audio, since that is the state most likely to misbehave — disconnect audio first (keep them paired).
On macOS the app uses classic Bluetooth, not BLE. Make sure the Nuraphone is paired in Bluetooth settings. If you built an older BLE-only version, note the Nuraphone does not advertise its control channel over BLE at all, so a BLE scan will never see it even though other devices appear.
This is the most common issue and it has a reliable fix.
While the Nuraphone is connected for audio, macOS's SDP cache can hand back the headset profile's RFCOMM channel (often channel 1) instead of the GAIA control channel (a higher channel, e.g. 14). Opening the wrong channel fails.
Fix: in Bluetooth settings, disconnect the Nuraphone (but leave it paired), then launch the app and hit Recover as the first action. The app now also selects the GAIA channel deliberately and will warn in the log if the device is still holding an audio connection, but paired-but-disconnected remains the most reliable state.
If a connect attempt has already jammed the Bluetooth state, fully quit the app (Cmd-Q) and relaunch; the first channel-open after launch is the clean one.
Key recovery needs Nura's backend. If it is offline (the product is discontinued) recovery cannot complete. If you already have your key, you can enter it by hand in the Devices tab and skip recovery entirely.
The stored key does not match the device. Re-run recovery, or re-enter the correct 32-hex-character key. Keys are per-device; a key from another Nuraphone will not work.
The Device tab has a Logs section (Copy All to export). It shows each GAIA command, the connection phase, and provisioning progress. It never logs the device key, account tokens, or the session key. When reporting an issue, the log lines around where it stalls are the useful part.