Why does her fur change?

[Auggie+Snowball+Belle]

Hi again. I feel like I’m posting a ton but oh well. For some reason, Belle’s fur is always changing. Like randomly a black line will appear on her nose and it’ll go away and then come back? And then there’s one on her side moves where it is all the time and the shape of the nose one changes when it’s there. I’m assuming this is normal but why does this happen?
When the nose one isn’t there


When it’s there (and how the side changes or seems to):

 

[SableSteel]

That's just part of the molting pattern. Chestnuts (like her) have a dark base color to their coat, so when they're molting and have two different fur lengths next to each other you can see the dark base color as a line between them (like in the nose of my profile drawing)