I'm running this gpu with a LG 34UM67 ultrawide display connected with display port cable 1.2 certified from Accell and freesync never worked without enabling also vsync.
Every game is afflicted by horizontal trasparent/blurry lines like strange tearing coming from the bottom of the display. I use only fullscreen and Vsync is off in all 3d applications/games. To stay inside the freesync range i use to cap my framerate under the maximum freesync range with the in-game limiter when available or rivatuner statistic server (for example 75 hz with 74 fps cap). This still causes me the issue described in the entire freesync range. Freesync works fine with a 390 nitro with the same settings.
I've also made a video to show the problem: