This is a bookmark that has been specifically designed to challenge your printers. It is very thin - from 0.5 to 1 mm - where the part that clips on the pages is just 0.5mm while the "50 micron" text is 1mm.

On the thin clip the text is carved so that the layers are just totalling 0.25mm.

If your print bed is not perfectly levelled, it won't print. Have a look at the skirt in one of the pictures: it is really thin (100 micron) and uniform. Get yours the same and it will print perfectly.

Sliced at 50 micron it is made of 19 layers (the first is 100 micron).