I have crafted three candy lanterns today and tried to add them to the open plot, and they are disappearing from my inventory but not being added to the running total to open the plot to the caramel apple castle.
I was not sure what happened the first time when I saw it happen and thought I was confused on my numbers. I just finished crafting one more lantern, looked in my inventory, saw it there, then I went to the open plot and hit use and it disappeared. So I can confirm I have had it happen twice today when clicking the use button on the plot.
I force closed my game and reopened, and there is no change to the quantity.
I tested the troll candy and that inventory count is still increasing correctly.