First option — gnome-screensaver

Go to Applications > Settings > Settings Manager > Autostarted apps

Click on Add, and enter whatever name & description you like, but enter gnome-screensaver in the [...]]]> There are 2 ways of doing this. One uses the already installed gnome-screensaver, and the other uses xscreensaver, which you’ll have to install.

First option — gnome-screensaver

Go to Applications > Settings > Settings Manager > Autostarted apps

Click on Add, and enter whatever name & description you like, but enter gnome-screensaver in the command box. This fixes the problem of the screensaver not starting when it should. This makes the screensaver app start when the computer boots up so that it will function correctly.

Second option – xscreensaver

Open a terminal and enter

sudo apt-get install xscreensaver

This will install a screensaver application. Now you must repeat the steps in the first option to make this thing start when the computer boots up.

Go to Applications > Settings > Settings Manager > Autostarted apps

Click on Add, and enter whatever name & description you like, but enter xscreensaver in the command box.

This was a very frustrating problem that shouldn’t exist, but does. Xubuntu has so many benefits that I think I can deal with this one little, easily fixed, bug just fine.