Today noticed a strange bug, fletcher's workshop produces 2 crossbows at the same time. Sometimes 1 crossbow, sometimes 2. I noticed when they drop off weapons at armory. Is this a bug or it is supposed to be like that? I just don't remember how it was in original Stronghold Crusader, haven't played it for 8 years.

Productivity goes up as you increase your people's fear of you. So if you've built things like torture chambers or gibbets they deliver more goods. Farmers drop off more crops per trip, lumberjacks drop off more wood, and in the case of fletchers they drop off extra bows/crossbows occasionally (how often depends on how high your fear level is).

If you've built things that increase their morale their productivity goes down.