Whether we want to admit it or not, we're never in "shooting shape" for those first few pins of each season. The first couple draws of each season feel a LOT heavier and more shaky than the last few draws of a season.
It's REALLY common, when guys pull the bow out for the first time each year, that they'll heel the bow a lot more than they normally would. Heeling usually ends up with higher strikes. It takes a few pins to get used to the draw weight again each year, and your wrist isn't conditioned to supporting the draw, so you might be putting more hand on the grip than you normally would.
It's also common that you'll try to watch the first few arrows of the year in flight, which inevitably, you'll end up pushing the bow upward slightly (your focus is on the arrow, so your body instinctively pushes the bow towards the arrow, aka, upward).
Either of these might be the cause.
Other early season High strike causes might be low shaft elbow, or loosening your bow arm upon release (lets the bow tip freely).