I’ve had this and it turned out to be a problem with the mesh normals and / or smoothing which was from imported CAD data. Try adding a smooth modifier+edit poly modifier and then colapsing it. Or even just replacing the object newly built one could be the quickest fix. Hope that helps.
Thanks for you advice guys but it turns out it is was something in my glass material. I used a different glass material and it was fine. If I get a chance to examine the original glass material and find out what cause dit I’ll let you know.