I've finally repeated this and can add my me too! Took me some time to get the "complete a work task" want - finally managed it by creating a Sim with the ambitious trait, and then two non-base-game traits, a non-base-game aspiration, non-base game activity likes, and no music likes.
That said, I was not able to replicate the quit job want not fulfilling - that one seems to work for me.
Product: Sims 4
Platform: Mac
Language: English
How often: only got the want one time so far, but bug with it happened first time
Current game: 1.91.205.1220
Packs: Cottage Living, Snowy Escape,Discover University, Island Living, Cats & Dogs, Get to Work, Werewolves, Realm of Magic, Strangerville, Jungle Adventure, Paranormal, Tiny Living, Moschino, Laundry Day, Bowling Night, Kids Room
Steps: Play with an ambitious Sim. It helps if you make sure there's nothing other than the ambitious trait to generate wants. Get a job and wait to get the "complete a work task" want. Complete a work task.
What happens: Want does not fulfill when the work task is marked complete.
What do you expect: Want fulfilled.
Mods: Not in this save.