Months before the Sony Xperia XZ2 Premium was unveiled, we saw the user agent profiles for two phones with 4K screens, the H8116 and H8166. So this could be nothing, but at the end of May TENAA certified a phone with the latter model number. It has 5.8" display like the XZ2 Premium, however, the page does not say anything about the resolution. The physical dimensions of the phone also match the Premium. Sony H8166, perhaps an Xperia XZ2 Pro, but probably just a version of the Premium However, the battery capacity - 3,400 mAh - matches neither the regular XZ2 nor the XZ2 Premium....
Source: https://www.gsmarena.com/tenaa_certifies_a_sony_xperia_that_may_be_an_xz2_premium-news-31493.php