The recipe is only going to be approximate because the author cannot know how much water your fruit has, what the temperature or humidity of your dryer's surrounding air is, how often you open it to look, how accurate the thermostat or heat setting on your dryer (or oven?) is, how carefully you measure if there were any measured ingredients.

Even once dry and cooled, a fruit leather can grab water molecules out of the air, causing it to become sticky and to soften. That is just the nature of sugar. Think how even a sugar bowl will clump when it hasn't been used for a while. That is because of it grabbing water out of the air. Or think of how uneaten hard candies soften over time, and may become so sticky that you cannot unwrap them.

Just dry your fruit leathers to your satisfaction, put them in a well sealed container, and even consider dusting them with cornstarch or orris root.

Ah, so it's a 'whatever it needs' thing. I'm OK with that. Thank you for the info. I guess I didn't really do anything wrong.