Hi! I understand that your JB4 app sometimes works and sometimes doesn’t, is that correct? To better assist you, could you tell me if the app fails to connect, freezes, or shows any error messages when it stops working? Also, do you notice if it happens in certain places or scenarios, like when you're in the car or away from it?

Meanwhile, I can guide you on some initial troubleshooting steps to improve the app's reliability on your Mac with OS X 10.15.7:

1. Restart your Mac and the car’s JB4 hardware — power cycling both can resolve minor glitches.
2. Toggle Bluetooth and WiFi off and on — since JB4 uses Bluetooth, sometimes the radio connection can become unstable. Disable both, then re-enable Bluetooth first.
3. Ensure your JB4 device is properly connected physically — check the wiring and connectors to the Positap or DB9 plug to make sure everything is secure.
4. Check for app updates on the Mac App Store — running the latest version can fix bugs.
5. Restart the JB4 app completely, or uninstall and reinstall it if it remains inconsistent.
6. Close any other apps that may interfere with Bluetooth connections.

If the problem persists, it might be related to the Bluetooth module or the connection to the car’s CANbus, which relays engine data. Sometimes, improper OBDII connector seating or interference from other aftermarket devices can cause intermittent failures.

Let me know if you would like me to walk you through these steps in detail, or if you can describe what exactly happens when the app doesn’t work, so I can tailor the help for you!