Autostart launchers work only once.
Using Xfce4 4.16.0 (Guix) with GDM and Xorg .desktop launchers don't work at all or only once.
Launchers don't work at all if created as text files as per freedesktop spec. If a launcher is created on xfce desktop by right click->create launcher and it is then moved to .config/autostart it will run once on next logon. However it doesn't run on subsequent logons.
Those launchers can be run by double clicking on them using the file manager as well as they are visible in Settings->Session and Startup->Application Autostart with trigger set to login.