Why do net carbs of individual ingredients not adding up in the full recipe total?

CCW

I am creating a recipe. I manually add up the net carbs listed of individual ingredients (5 ingredients), and it does not add up to the total net carbs shown for the full recipe.

Ingredients and the according net carb contained:

100g of chocolate - 13.3 g net carbs

4 medium egg yolk - 2.1 g net carbs

50g of cacao powder - 8.3 g net carbs

400g whole milk - 20 g net carbs

200 heavy whipping cream - 5.5 net carbs

I added the net carbs of the individual ingredients, 13.3 + 2.1 + 8.3 + 20 + 5.5, and yielded a total of 49.2 g net carbs.

I expect to see 49.2 g net carbs to be accounted for in the full recipe energy summary (the last tab). But it is showing only 30.5g net carbs instead. 

Please help.