Rhino is all of a sudden started working very slow and in rendermode it shows some objects with VERY jagged edges

I have just upgraded my Mac to Mojave
and for a strange reason it has started to show shapes in render mode totally jagged. these are VERY simple mock up models. i have tried the settings but with no change.

My mac is a 2017, 3.8 Ghz Core i5. 48GB Mhz DDR4-Graphic Radeon Pro 580 8192 MB

Looks like a distance from the origin kind of error, How far away is the origin?

try refreshshade command with the object select

Thank you for the answer but Not working! if i duplicate an edge in a circle and copy it and then loft it. just before i click ok to final loft it, it will show the form completely square and jumping around if i toggle the frame.

And when i click ok! it will think a bit and then turn perfect.

Is the object VERY far from the origin (world 0)?

yes the element is in an architectural 3D plan i have received from a client. and it is not in 0,0 origin

Thats strange! you are right Helvetosaur. I move the 3D plan to 0,0 and it is showing the elements fine??
do you know why this is happening!

Yes, this is a typical phenomenon… There is no real workaround.