Your fill color is to close to the outside border of the lineart.
The way Photoshop render a stack of layer and an actual merged image is different.
The zoom and filtering cause artifacts because it is rendering different pixels from different layers but when you export it (or merge) the final image is not made of two diferrent things and you get the right result.
Well I don't think you want to know about the math stuff behind this so in short, will work when you export it or reduce your fill layer.
