You might find interesting reading over at the
They have a forum within devoted to 120mm folders.

I am new to folders and don’t profess more knowledge than I have read here and there. For confirmation, both of the suggestions mentioned above are often repeated there. Another idea that might help is that you should advance the film just before you are ready to take the next picture rather than just after you have taken the first. The logic is that in these old folders the film is not held tightly wound in place. If your next picture is some time in the future the film may move around a bit and not be tight. This can cause some overlap of image as well as blurred focus. If your images have good focus the above mentioned ideas are more likely the problem.

John Powers