Neither of these. I remember Werner saying that something is running out of resources. Reopening sketcher or even restarting FreeCAD usually helps.
As you can see from your FreeCAD infos, you use a 64-bit FreeCAD. I don't think it is the hardware resources, it is rather something in one of the used libraries such as Qt (I don't know which library finally handles Sketcher's 3D view).
I had the same problem on similar machine (occasionally) and the solution was the same, so glad that it isn't only me