I tried WillR's problem in V19.0 Build 20.4 and to get the "C" snap to not work, I had to uncheck Degenerative Faceting.
When Degenerative Faceting is checked, then the "C" snap works on a solid 3D Cylinder.
I tried this in RedSDK and GDI.
I'm not sure what is wrong with WillR's version 19.
Designer, Deluxe, (Professional, Expert, Basic), Platinum
Windows 10 Pro (1903), 64-bit