Mixing some sour flavours with milk (especially hot milk) may be tricky. Cold milk is curdling with Pomegranate and Cranberry syrup, while hot milk is curdling with all sour flavours.
It mainly depends on quantities, the type of milk you are using and how you do your recipe. Pouring the coffee before the milk will usually prevent it from curdling.
You can also reduce acidity by mixing the milk with a MONIN sauce or with another non-sour MONIN syrup (for example 20 ml Macaroon syrup with 10 ml Blackberry syrup, or 15 ml Chocolate sauce with 15 ml Le Fruit de MONIN Red Berries).
A recap table with details for all flavours is available upon request at monin@monin-france.com

This may be caused by any naturally occurring fruit oils, pulp or pectin contained in the MONIN fruit flavouring. This should dissolve once shaken and is not a cause of concern.