I play with mundane zombies mod wich removes the special zombies
That probably makes the mission un-completable. You have to kill the mentioned shocker zombie to complete the mission. But blocking those monster types also prevented that one from spawning, so it’s not there and can therefor not be killed.
Looks like a nice bug you found there. Zombies with special properties (like having a mission ID) should probably spawn regardless of the blacklist.
and how to get rid of this one with out lieing the NPC
Set the mission id of a random monster to the id of the current mission, then kill it. This probably involves some editing of the save. Alternately: use the debug menu to get rid of the truth teller trait (maybe add some other traits that increase your chances to lie successfully), lie about the missions, revert the traits.