Your radion buttons use
response.correct as value which is not unique, your question contains multiple responses with the same value (
undefined as you don’t have
The right answer is selected and your value is
true. If you now select a wrong answer, your value gets updated to
undefined. As two responses have this value, the second wrong response will be marked as selected (but you have selected the first wrong response).
You could use the index of each response as value (which is unique for each question) or add a unique identifier to each response.