In a current environment where this works and you come across one machine or a range of machines that will not push the PXE boot advertisement. Assuming you’ve already checked off the following.

1) You’ve set up your collection.
2) Your machine is recognized by SCCM, and in the desired collection.
3) Your boundaries set for the machine location are set.
4) You’ve configured your Task Sequence with your boot image.
5) You’ve advertisement your Task Sequence to the collection set you desire.
5) Your advertisement is set to PXE boot.
6) You’ve cleared the last PXE advertisement from the object.

If you’ve determined all your configurations are correct and this same process works with other machines in other boundaries to to delete the boundary and recreate the boundary.

– Harry Caskey