Black pipes are seen in a Global Collection between a device model and a container model such as a Network or LAN container model. The probable reason is in the normal topology under the Universe, the device is actually contained within the container model. Navigate inside the container model and see if the device is contained within it.
The device model is contained within the container model in the normal topology under the Universe. When creating the Global Collection, the user is trying to show the device and the container model at the same level when they are not.