Recently I was running a game and my players were in a fight with a Young Red Dragon that was climbing a wall. One of my players was able to inflict the prone condition on it. We then had the conundrum:
Does a creature with a climbing speed that is climbing a wall, remain clung to the wall when knocked prone or does it fall from the wall, to the floor?
I have seen questions in regards to this with Spider Climb but that is a magical effect so the rules may differ.