Black screen during PVP
Some people report similar issues in the bugs forum, though not specifically to do with PvP. One player has been reporting that character switching during the pre-match countdown would crash the client though.
I’d try turning off NVIDIA ShadowPlay, any GPU temperature monitoring, tools like RivaStatisticsServer or AMD Afterburner, and otherwise anything that gets into the graphics pipeline (eg: voip overlays, DPS meters, reshade style graphical enhancers) and see if the problem still occurs.
I also notice that the (default) F12 key when pressed will bring up the logout, change character dialog box, and you can click the buttons but nothing happens.