Can an item contain Kitniyot without being labeled as such by the Hashgacha?

What causes an item to have conflicting Hashgacha statements, with one stating it's Kosher for Pesach and the other indicating it's not?

Are dairy products labeled as Kosher for Pesach automatically Cholov Yisroel?

Is it accurate that Diet Coke contains Kitniyot?

Link to website with visuals:https://sites.google.com/view/kashrusbeintheknow/audio-classes/pesach-purchases-for-beginners-beyond?authuser=0