@erik6 the issue you are seeing is duplicate geometry in the same place but with different materials. Zooming in and out or looking from specific angles will change which object “wins” to be drawn “on top”.
For instance in the file you shared window marked W-3.1 FK-205, which is a group. Select that and run _Isolate. Then _Ungroup. Select the window pane, you’ll see that Rhino asks you which of the two objects to select:
Select either and move it away so you can see the other object.
Do the same with the frame:
So, to fix the issue you have to go through your objects and make sure you don’t have duplicate geometry in the same place. Remove those that are not supposed to be there.
