I have just noticed this on the top of my saddle bar and where the seat post clamp is. Is it a crack probably caused by the saddle pressure?
Doesn’t look like a crack, looks more like a surface void that formed during the resin injection molding. These types of imperfections are not uncommon, especially on the inside of the frame where you can’t see them. Less common to see them on the outside as they are usually caught in quality control inspections. While they are not ideal, as areas with voids will be somewhat weaker than areas without voids (depending on the size and depth of the void), they are not critical like a crack.