Why is my right window mullion partially white?

Support Lighting and Rendering
1

I duplicated the left mullion and glass and moved it to the right but I still get this render error.

Attachments

Why is the right window mullion partially white.jpg1917×1079 566 KB

2

I moved all the objects in my scene to the left 20 units and re-rendered and the partially white mullions are gone. Why would this happen?

Attachments

moved objects to the left and white mullions are gone.jpg1914×1078 338 KB