This issue is due to an outdated OS version. Always check and update your Operating System to its latest version. Microsoft released an update with Bluetooth connectivity fixes: https://support.microsoft.com/en-sg/help/4458469/windows-10-update-kb4458469
If the issue persists after the update, do the following:
- Uninstall all Razer software.
- Switch off the Bluetooth of Razer Atheris and unplug the dongle, if applicable.
- Go to the "Device Manager".
- Click "View" and select "Show Hidden Devices".
- Open each category in Device Manager and uninstall all items with "Atheris".
- Restart the computer and reconnect Atheris.