Today I emailed Gigabyte on the matter:

Dear Gigabyte: 

I have purchased the Club3d CAC-1070 Displayport1.2 to HDMI 2.0 active adapter. This device should enable the Gigabyte R390 to output 4k@60Hz to my Samsung 4k television over HDMI. However, the framerate is capped at 30 Hz.

I have tested extensively with different:
– drivers
– cables
– OS
– GPU Firmware
– Motherboard Firmware
– Other GPUs (R290) and Laptop
– Other configurations entirely

Be advised, I have seen my TV, Cable and CAC-1070 adapter work in combination with an other GPU. Therefore I will have to conclude the problem is isolated to my Gigabyte GPU.

Please attend to this thread I started on the club3d forums for further information and photographs:

https://insights.club-3d.com/thread/the-cac-1070-amd-r390-samsung-ju6650-windows-10-64x-challenge/

My username on that forum is ErikG.

I hope to hear soon on any advice or solution you offer to my case.

Regards,

Erik