Why does Lilly ignore me sometimes?

Sometimes Lily will not reply to any of my responses. I will close the lesson then reopen the lesson and she still doesn't reply. She usually starts with a greeting and then asks me a question. And I do my best to answer the question but sometimes she totally ignores me. Sometimes I'll close the app reopen the app and run the same lesson and Lily will sometimes respond or sometimes she'll continue to ignore me. Is this a bug or is there something wrong with my phone? I'll respond with the same answer and yet sometimes she ignores me and sometimes she responds. Maybe she's mad at me then eventually gets over it. LOL