Did you hear back from LG? I have just purchased a 29UM67-P and have the same grey line issue when using freesync with 2x390s in crossfire. The card doesn't seem to make a difference though.
I actually just watched Linus' review of the 34UM67 and the grey line appears on that too by the looks of it, you can kind of see it in the image below:
I could return it to ebuyer, but I'm worried I'll just get another faulty one, Id rather send it to LG and know they'll update the firmware and send me back a fully working model.
Sam0r got a reaction from hugotheholder in LG 29UM67-P Grey Pixels