Do you have a link to your site and I will take a quick look to see if it’s a layer z-index (layer levels above each other).
Update: I just setup Celestial Reloaded on my local test site and imported the LayerSlider plugin and slides, added it to the “Showcase” widget position, and the Curve is showing for me.
Make sure the slider is being loaded in the “Showcase” position, but also make sure that the curve is not disabled in your theme option settings either.