RE: OUCH!!! Arm Slap
Whenever I get stung by my compound, it's always because of string/cable creep. Always. String creep will increase your draw length, lower your brace height and, since there is less tension on the string, it will 'bullwhip' further forward than nomal.
Check your brace height and axle/axle measurements and make adjustments to get them back to spec.