One of the Proti Thin bars I bought has invert sugar listed in the ingredients. Are we allowed to have this? Does anyone know how this will affect weight loss on IP?

From Wikipedia:
Inverted or invert[1] sugar syrup is a mixture of glucose and fructose; it is obtained by splitting sucrose into these two components. Compared with its precursor, sucrose, inverted sugar is sweeter[2][3][dubious – discuss] and its products tend to retain moisture and are less prone to crystallization. Inverted sugar is therefore valued by bakers, who refer to the syrup as invert syrup.[4] It is similar to high-fructose corn syrup.

So it's just a form of sugar, and needs to be counted as such. HFCS may be implicated in metabolic syndrome because our bodies do not recognize it the same as simple sugars - less 'sweetness satisfaction'. Invert may possibly act the same way in our bodies. Your choice, but be careful as it is another name for 'sugar' which IS a simple carb.

IP also uses sugar in products. If the nutrition of the bar fits all the parameters of an alternate that meets IP standards it should be fine. Sugars are just a kind of carb so the net carbs will be what you focus on along with calories, calories from fats and protein.