I saw a high speed video at the Milwaukee ww'ing show last spring that
showed that exact problem, vendor was selling blade stiffeners. Anyhoo the
blade when it starts to distort takes on a potato chip shape as it actually
starts to run in two separate planes. I guessing those hotspots are where
the distorted plane was beginning and ending. I'm also guessing that they
eventually would work around in a full circle with continued use. But hell
I've been wrong before... could be just a flaw in the steal or machining.

EJ