It's hard to see your stroke from here. But my experience has been that when a swimmer's leading arm drops when they breathe, it's usually because they are raising their head to breathe and are pushing down with their leading arm to push their head and shoulders up.
Do you breathe on only one side, or do you do bilateral breathing? I ask because you only mention having the problem when you breathe to your left, and I'm trying to determine whether that means you don't have the problem when breathing to your right, or whether you never breathe to your right.
Also, do you have any problems if you roll to your interrupted breathing position (also sometimes called "sweet spot") to breathe?