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.
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.