Can’t get network applet back in Ubuntu MATE 18.04

After upgrading from Ubuntu MATE 16.04 to 18.04, I can no longer get the network applet in the notification area.

This answer shows how I solved this in 15.04, and this solution survived the upgrades to 15.10 and 16.04, IIRC without any need for further intervention.

On 18.04 this no longer works:

• ~/.config/autostart/nm-applet.desktop was no longer there, so I copied it back from /etc/xdg/autostart/. The edits described in the original answer no longer apply, so I left the file unchanged. Even after login, the applet does not come back.
• When I try to launch nm-applet manually from the command line, it just gives me the message Gtk-Message: 13:48:39.885: Failed to load module "topmenu-gtk-module", then exits and no network applet is ever displayed.
• The notification area, as indicated in this answer, is active—I see the volume applet.
• If it matters, I have the Traditional panel layout.

Additional information: on another computer (also upgraded to 18.04 from 16.04 but using the Familiar layout) the applet is still there.

What gives?

Solution 1:

I don’t know what it was, but I was able to get the network applet back by going to System > Preferences > Look and Feel > MATE Tweak, and in Panels, first saving the existing layout, then re-selecting the Familiar layout.

Note that this will delete any customizations (if you’re not ready to part with them, be sure to keep a backup around). However, now I have the notification area with Bluetooth, network, mail, battery and sound icons (previously there was only the sound icon), as well as the combined Settings/Shutdown icon (previously I had the Shutdown icon instead).

Since there have been doubts about this: this solution has also survived multiple reboots.