Updated for 6.0:
Tethered caching now requires you to select a specific device group and does not work on your whole environment
When a Device responds with Waiting for Network Tethering it usually means the Tethered caching settings in Organisation > Settings is enabled.
The installation will only start once the device is connected to a MacOS device, if this is not something you want you should disable these 2 options.
For more information on Tethered Caching please refer to Apple's official documentation on this: https://support.apple.com/en-gb/HT207523