Forget trying to make them perfectly crispy. Is this even a real problem or just something people overthink? @jenny_brown58 might be right that zucchini has too much water. It will always steam in there no matter what you do. Salting them first helps a little but it's a lot of effort for a snack. Maybe soggy zucchini chips are just how they turn out and that's fine.
Ugh, Jenny_brown58 is onto something with the water content. You have to cut them crazy thin, like almost see through, or they just steam themselves. I found tossing them with a tiny bit of oil and skipping the parchment paper helps a ton, lets the air move better. It's a pain but that's the only way mine get kinda crispy instead of sad and wet.