Well, I considered planks mastered when I reached 5x60 with that form and I moved happily to one arm planks. However, I felt like I was spinning my wheels on them, and I decided to take a couple more videos from different angles.
As you can see, my back is more visible on my right side. Now, I don't know if that is a muscle imbalance, not enough protraction on one side or something else. From what I see I'm also crooked, but I FEEL straight and protracted equaly on both sides. I'm really at a loss here, any help would be much appreciated.
My scapular shrugs also seem to have the same problem.