This randomly happens when smoothing sharp corners. Note that it's only on part of the edge. An indent I can't smooth out for the life of me! what causes this? [postimage id="6000" thumb="900"]

Not too sure but it could be an air bubble or the frosting underneath that isn't perfectly smooth.

I recently bought some flexi smoothers online, and those work magic! they'll get rid of any blemishes, big and small. Here's the link:

https://www.etsy.com/uk/listing/243225470/pink-8-piece-flexi-acetate-smoother-set?ref=market

It's not an air bubble! Also checked! And yes I have these flexi smoothers! I also notice some professional cakers have a little lip. 

Could it be that the fondant has not been rolled well?  OR is there a dent in the cake? 

I get that same thing I think, for me it's a dent from when I first lay the fondant onto the cake. If it shifts a lot from its original position, I get a ghost of the corner. 

Cake was 100% smooth underneath. Also has a very sharpe edge with buttercream. And the fondant is smooth when rolled out with all the air bubbles popes. This is so strange. 

Why can't you smooth it out?? What happens if you try?

It just slightly smoothed out and when I moved to the next part it would reappear.

This happens to me - its from when you first lay the fondant on over the cake ... and then you start smoothing out the top.  Its the edge that first goes over the edge, but then as you smooth the top it stretches down a bit.  I don't know how to stop it unfortunately!