Did you try making sure Sacrosanct is loaded below other mods that modify PlayerVampireQuestScript and/or DLC1PlayerVampireChangeScript and making sure there aren’t any loose copies of the scripts in your data/scripts folder? Sounds like conflicting mods
Have you tried changing the load order of your mods? Might be as simple as that.
Maybe you need to rebuild your merged patch and/or bashed patch.