Mrs Greenpen suffers the same problem with peppers. If they are raw she suffers discomfort after eating them but when cooked it's fine.

I think that in prepared meals they undercook the potatoes so they do not go soggy or break up. If they get this wrong by a fraction then the meal you eat still has raw or partially cooked potato tissue and this causes the problem.

Undercooked potato and overcooked steak/fish; oh dear!