After I completed the part of the Dark Brotherhood where you have to hide inside the Night mothers coffin Iam told to talk to Nazir for my second list of contracts. However the dialouge option to start the contracts is not there. I later descovered that its because one of the contracts that I was supposed to kill after I talked to Nazir was missing from the game...Hern, the vampire!

This prevented me from getting the dailouge option to start the second list of contracts. Dark Brotherhood questline is broken.

Update...

Ive started a new game and I found out that "Hern" is STILL missing and nowhere to be found in Skyrim. Has anyone else had this happen to them in every playthrough?