I think Fed Ex Ground (which was once RPS) is part of the Fed Ex proper. Fed Ex Home Delivery is another matter and uses contract/non union drivers.
The tracking system is the same, etc. I use Fed Ex a lot and they have never left a sticky unless to inform me they attempted delivery but did not deliver since no one was home. When they deliver, the leave the box on the porch but never a sticky note.
Is it possible the driver stashed the box in too good of a hiding place?
It is possible someone stole the box. It is also possible the driver did not leave the box and will re-deliver today.