Concerned Xperia owners who were experiencing intermittent stripes appearing on the displays of their flagship XZ1 and XZ2 phones have been told by Sony that static electricity build up is the cause. The stripes aren't considered a defect and aren't a sign of any pending malfunctions.
https://www.notebookcheck.net/Sony-Xperia-screen-stripes-explained-with-electrifying-description.309818.0.html