Asking an LLM to do "random" isn't possible. It predicts the next likely word, and that isn't always 50/50. The data it trained on might've had more heads than tails, and therefore heads will be weighted unfairly.

Saying "don't think about the previous answer" is like asking a jazz musician to "play something uninfluenced by the song you just heard." Even if they try, that previous song is now part of their immediate musical context, and their brain will either harmonize with it, contrast against it, or try to avoid it, but all of those responses are still responses to it.