A face mask can make you lose your anchor and shoot high...Not using a peep or 2 nocks on the string to center your pin can also make you shoot high...As mentioned simply dropping your arm and not bending at the waist can makd you shoot high...

Not tuning your bow to broadheads after shooting field points can also make you shoot high, low or left or right...

Shooting at an alert deer can cause the deer to crouch to sprint off can make you shoot high...(Actually you don't shoot high the deer moves before the arrow gets there)...

As mentioned, get in a tree with your hunting attire and broadheads and try shooting...

Don't ask how I know these things...