There are a few ways lxde autostarts.
xpad under Lubuntu 16.04 also uses: /home/$USERNAME/.config/autostart/xpad.desktop
I notice that under Lubuntu 16.04's light-locker is also launched this way. But under 18.04 light-locker is started some other way.
A possible quick fix/work around for xpad would be to just create the /home/$USERNAME/.config/autostart/ directory during the xpad install.
Just an fyi -- xpad looks like a nice app, but I don't use it. So I may not be commenting further on this particular bug.
There are a few ways lxde autostarts.
xpad under Lubuntu 16.04 also uses: USERNAME/ .config/ autostart/ xpad.desktop
/home/$
I notice that under Lubuntu 16.04's light-locker is also launched this way. But under 18.04 light-locker is started some other way.
A possible quick fix/work around for xpad would be to just create the /home/$ USERNAME/ .config/ autostart/ directory during the xpad install.
Just an fyi -- xpad looks like a nice app, but I don't use it. So I may not be commenting further on this particular bug.