There are two ways to consider this: First, the mind is not yet fully trained and under control, so it is not responding to the higher will as desired. We would expect that as a meditation practice is cultivated and skills developed, these aberrations will come under control.
But then, there is also the possibility that negativity is being stirred up and is interfering with the process. In counseling, after having processed feelings behind an issue, we sometimes will suggest that the client visualize a positive outcome. But we do this with the understanding that if there is still suppressed negativity, visualizing the positive will not be fully effective, and will most probably only incite the suppressed negative and will produce images contrary to the desired outcome. When that happens, we just return again to the negative and apply the process. The positive visualization has then served as a tool to access the suppressed negative.
Maybe something like this is happening here. In trying to visualize protection, vulnerability results, even before you get into more specific processing. So the strategy would be to not get upset that the induction is not going according to plan, but just regard it as successfully stimulating negativity into awareness, to be processed with the steps. Take all the images to a feeling level and work with the feelings. You can still witness the experience without identifying with it, which is the most important element.
It's a good sign that you are sensitive enough to be able to perceive these subtle inner states. You appear to just be encountering the opposition to inner work that I talk about in my books.
