This sort of behavior is typically related to the graphics card and its drivers and isn't a SketchUp bug. This is especially the case when the behavior changes after a period of use. SketchUp 2017 requires graphics cards that are up to handling OpenGL and handling it well. There's no offloading the graphics card's work to the CPU as in older versions. With Windows, the user can try to update the graphics drivers from the card's maker. With Mac it's not usually possible to do that. The graphics drivers are part of OS updates that Apple pushes with some frequency.