Please check which quest number it is, so we have a better idea which one is bothering you. Could be that you have taken trades from neighbors when you were asked to take trades from the wholesaler. Trades taken will not count then.
I have also had the situation where I completed the task, and it did not appear to register against the quest, until I went to a different screen and back. Probably not the case here, but worth mentioning.
hello @Demesne, we sometimes skip over the wording used in the quest, checking the wording first might be a good idea. Do drop by and let us know how it went for you. If you still have issues with this, you can contact support in-game (when right-clicking your mouse a pop-up window will appear).
I have not had anyone say they have had it again but i have already told them to just refresh to solve the problem. It only seemed to happen if the player was online when the province finished being scouted. I have not heard anyone mention having a problem like the OP.