Nightingale Legacy Portal
It appears that Aid quests that pop up in Herbarium and later realms have an excellent chance of not spawning any workers. Perhaps they were killed by roaming wildlife. In any case, you can still spend all your resources to construct buildings fully but that locked chest remains so.
I had this happen a couple times too. Not sure if the survivor dies or just doesn't spawn. But since you have to talk to them to initiate the Aid quest, the chest won't pop even if you build everything.