Hi,
I’m exporting this simple element to SVG, but for some reason the masks applied to the outer circle is ignored.
This is what I see in Sketch:
This is the exported SVG
These are the layers inside Sketch for the element
I tried using just an arch instead of a masked oval, but since there is not Inside/Center/Outside setting for open shapes, it’s really difficult to match the container.
Hmmm, curious… 
The setup I created below outputs an SVG as expected, with no issues.
I’d like to take a look at this for you. Could you share the Sketch file please? 
One thing to note, is that I’m using combined shapes for masking since I need to get “one quarter circle” too.
Hey there. 
It’s a very quick and easy fix.
Instead of having the entire mask layer itself set to invisible in the Layer List, make it visible, but then set the Fill property to none to get the same effect.
Now when you export the SVG, you’ll get the result you require.
Great! Thank you very much
