My experience on seizures not preceded by knocking is the rings seize to the bore. Some times they will free up if you whack the crank shaft bolt or the blade.. Wise to squirt some lubricant in the cylinder first
I had the same problem and fixed it by loosening the valve lash. Put a compression gauge in it and watched as I loosened the lash. Didn't have to add to much lash to get the compression up. Started really easy. I have had the worst problems with compression release on the Kawasaki's.
Personally I don't like the design. I would propose that you try to operate the mower in a manner where the discharge is always blowing into prviously cut area and never into uncut area