Could it be that your lovie is scratching at his ear, which is causing an inbalance in the inner air canal vs the air pressure outside of his ear, which is thus making him yawn???
Here's what I mean, only that it's a human that is causing the inbalance
YouTube - Birdzilla yawning and grooming
As for the mite-protector, I agree, keep it off the cage away from your bird.