If you are missing one fossils or more try to dig up in dessert in morning then if you have enough fossils for about 10+ it's 100% sure that a missing fossil could be found and don't waste the time if you had a mission from morning to evening if you are stuck in a mission or nothing to do try talking to them at home or school. That's all i know cause surely i had 100% progression and nothing to do in 0.6 for now still waiting for the next update. Keep it up!