Both displays are ASUS VP28UQGL and they work fine under Linux. When I open a game in Windows, this happens:
It worked fine when using a FreeSync and non FreeSync monitor. This started happening when I upgraded to a dual monitor FreeSync setup. The only way to prevent this issue is to turn off the second display in Windows.
I'm running the latest AMD drivers, display and mobo drivers and using an RX 580 ASUS dual 4gb graphics card.