Desktop Icons disappeared on Ubuntu 18.04

I had the same problem, all files on the desktop were gone.

I then ran nautilus-desktop from the terminal and the files were shown again.

So what happened? I had run

usermod -G new-group my-username 

and forgot to include -a in the command, thus removing myself from all other groups. I had logged out and in again, then observed this.

On a Ubuntu 18.04 system, I followed these steps:

1. I opened the "Desktop" folder in nautilus.
2. I then dragged all the ".desktop" files to my desktop.
3. When a dialog popped up and asked whether to trust those files, I answered in the affirmative.

On Ubuntu 18.04 desktop icons are provided by nautilus-desktop which is a part of the nautilus package, not by the "Desktop Icons" extension as you have suspected. So it seems nautilus-desktop is not working correctly. To fix the issue purge and reinstall the nautilus package and restart your computer.