1) Airbnb wants to make sure you get booked, at any price. For them, any number of dollars is better than $0. If they get $70 a night for booking 50% of the nights ($1050), and $50 for booking 100% of the nights ($1500), which one do you think they will encourage? Most hosts here just ignore their recommendations, especially those that have seen for themselves what the market will bear.
2) Somewhere on your calendar, there is a $68 price set, either on some random day, or in the Settings where you set the default price (Calendar/Pricing settings/Base Price on IOS). If you are sure this isn’t the case, call Airbnb, as it may be a software defect of which they may or may not be aware. Also check any discounts you might have set.