My FW16 has the display currently locked to 64hz according to the Windows display properties and confirmed by ufo test. I tried reinstalling drivers and updating the bios but it isn’t fixed.
One difference I notice is that it says it is using the Microsoft basic display driver on yours and the 780M on mine. What does it list on the Adapter tab next to the monitor? And have you tried installing something like AMD Adrenaline and using that to find/install drivers?