If your flapjacks are coming out too crunchy for your liking, then the most likely reason is that you have baked them for too long in the oven. When you remove the flapjacks from the oven, they will still be soft and will harden more as they cool. So don't be tempted to keep baking them until they are fully firm.
Rough cooking times for flapjacks are 20-30 minutes for soft and chewy, 30-40 minutes for medium-soft and 50 minutes for crunchy and firm. (Naturally, factors like the size of your baking dish, the size of the batch you are making, and your oven temperature will affect this).
You might also have overdone the butter, sugar, syrup, and peanut butter in the first couple of recipe steps if your flapjacks are too hard. This reduces the mixture to more of a caramel. You only need to melt the ingredients in this step, not simmer or boil them.