Removable Drive Menu is a status menu for accessing and unmounting removable devices. The Removable Drive Menu status menu is accessed by clicking its icon in the Panel notification area as shown in the below screenshot. The Removable Drive Menu GNOME Shell extension can be installed from Ubuntu Software.

It appears that this GNOME Shell extension extension is sometimes either delaying or interfering with the normal loading of other notification icons in the GNOME shell Panel. This problem is not necessarily related to the Removable Drive Menu extension specifically as other GNOME shell extensions have been known to cause the same problem. The way to restore the missing networking icon to the Panel is by running the following command:
setsid gnome-shell --replace
After it comes back press the Enter key before closing the terminal.