The crysals may have developed after ,or they may have been small andkind of stretched back into shape enough that you wouldn't notice. The clear coat isn't flexible ,so when the bow was flexed it "crumpled" at the site of stress. When the bow straightened the "crumpled area was no longer adhering to the wood,forming spikes. That's one scenario. It could be that they aren't crysals at all, and just finish incompatibility. Have you checked your tiller to see if it is weak or hinged at the site?