I know it's a couple of months after this post, but one factor that wasn't mentioned specifically (alluded to in passing) is when you don't have enough outhaul, ie a "baggy" sail, it tends to pull you over the nose into a catapult rather than create a nice laminar flow over the sail pushing you and the board forward smoothly...

Can't stress enough how important your rig setup is - a few centimeters more or less downhaul or outhaul, a few centimeters forward or back on the mast track, it makes a big difference to your sailing. Best tip I can give is to make adjustments when you are sailing - stop in the shallows, or go out on the beach and make the adjustment, don't just keep sailing because it seems like an effort to stop and make the changes. And remember that the conditions changes over time while you are on the water, you should keep your rig adjusted to the conditions.
My 2 cents worth...