do you have a lot of designs displayed on the ground? the more designs the less space the game has to put them so you can go long amounts of time without seeing any? this is the only reason I can think of, although I am not a AC expert lol hope you get some more answers.... and fossils!
Use the D-Up. As the camera views up trees and buildings in front of you will disappear. You should always get 3 fossils and one pitfall per day. If you leave items on the ground, then you can lose a fossil.
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