To resolve this issue, follow these steps:
- When the pop-up "System Extension Blocked" appears, click on [Open Security Preferences], not [OK].
- Click on [Allow] button next to the message "System software from developer "silex technology, inc" was blocked from loading".
If you clicked on [OK] first (instead of allowing it in Security & Privacy), the pop-up may return when the computer is rebooted or the OS is shut down. If this is the case, please reinstall the Network Monitor and follow the steps above.