Jigsaw block not working as expected

Hi! I'm new to jigsaw and have followed a lot of tutorials.
As you can see here, my parent/child jigsaw couple is supposed to touch.

But, somehow, it just doesn't and leaves one block space, and afaik jigsaws are not supposed to work like this.
Where there are natural-generated blocks, air is not placed (I didn't place structure voids) and that results in a underground invisible structure.
Even though the type is rollable, I can generate it over and over and will always generate with the same rotation.

Pls help me I'm going crazy 🙂