Hi I'm having the same problem when exporting 4K footage with Lumetri grade on the footage. I've used every conceivable method to remove the lines but they are still here. The same problem happened on the iMac and the MacPro and on all three versions of CC, 15,17,18
Might have to ditch Premiere Pro if they still haven't sorted this issue out. Its costing my time and money and I can't export final product with this sort of issue going on throughout the exported video.
@mediaworks did you get this fixed?