There are many factors that make the APY of a coin decrease in price because the price of the coin being farmed has fallen in price.
If we farm when the coin price is 1 dollar and then the coin price drops to 0.1 dollars, our APY is reduced.
At that time, maybe the APY was correct and the rewards were also true with coins, but if the coin went down, the APY of the price decreased but the total token rewards were correct.