This happens with other plugins as well, for example Arturia Jupiter 8 in Cubase 10 HiDPI mode gets cut on the right side of the keyboard, and hovering mouse over the GUI activates stuff in wrong places, right from the actual mouse pointer.
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 developers now.
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.