As a temporary workaround, after you open the S-Gear UI, if you click the blue power button off and back on again, it should redraw the missing part. You have to do it every time you open the S-Gear UI, but it’s at least a temporary workaround. It worked for me, please let me know if it does for you too. I raised a support ticket and they could recreate it, and I was told it’s been passed to the (Steinberg) developers now.
For me, it works fine in Cubase 7.5 - 9.5, and worked with the first C10. If you try the S-Gear stand-alone, it should work fine. It’s only when used in the current Cubase 10.