Those that break often have dead or diseased limbs. Disease may be caused by infestation of insects and parasites. Insects and parasites gain entrance by scrapes and scratches left by bobcats and bears - as signs of dominance, in the attempt to draw sap. Not all bobcats cause tree disease. Then perhaps we shouldn't rely on scientific method.
Most results only show a correspondence.
It is time to take anecdotal evidence a lot more seriously. I can't emphasize this enough. This disease devastates. Scientific method may be widely accepted. So is Buddhism, Christianity, Islam, Judaism and Hinduism.