Could combinations of foods cause different allergic reactions?

Too many variables: You would think that mixing all kinds of foods together and cooking them would cause some novel combinations that may be allergenic but we don't really know. That's for actual food allergy but combining foods can potentially cause GI intolerances.

Possible: Anything about food allergy is likely possible but I must admit that there has been no study ,to my knowledge, addressing this issue. Theoretically one can postulate the such allergic combination can occur. Do note however that cooking in general reduces the allergenicity of a food and perhaps that's the reason why we have not observed this type of problem