Does anyone know why the unsweetened and unflavoured has more calories per 100g (423) than the vanilla (410)?
No idea really, my guess would be that the amount of grams you add to vanilla in sweetener / flavourings contain less calories than the additional contents added to make them both 100g.
e.g. there may only be 95g of ‘Huel’ in 100g of vanilla the rest being lower calorie sweetener / flavour.
I may be completely wrong though and the figures are examples
Yes you are right the flavour system and sweetener are less calorie dense than the other ingredients.