The reason why soluble and insoluble fiber may not add up to dietary fiber is because soluble and insoluble fiber are not mandatory nutrients on a food label. Therefore foods don't always have data for these 2 sub fibers. When that happens there can be foods in your recipe that don't have a value for these 2 types of fiber. To see which one could be the reason, open your recipe and on the recipe tab where all the ingredients are shown along with their nutrients.
Right click in the white space there and select nutrients then pick soluble and insoluble and then you will see which ingredients don't have this value. Your option is to fill in that value for the ingredient (by opening the ingredient). Please note our foods may also not have soluble or insoluble fibers since its not a mandatory nutrient so many food sources do not provide it.