4k grabbing with gopro hero 6 and av.io 4k

Hello. I’m trying to grab 4k video from gopro hero 6. I’m using default hdmi & usb cabels from av.io box.
Unfortunately I can only grab 2560х1440 without black borders by 30 and lesser fps too. Changing to higher resolution returns a black wide border around video frame. Looks like 2560х1440 is maximum possible resolution.
firmware 3.2 (3.3 has only Improved sleep and power management support and is still beta).
Have tested with ubuntu 16.04 in OBS & qv4l2.
This thread said gopro 5 supports 4k via hdmi https://www.epiphan.com/forum/t/which-4k-cameras-give-clean-output/60.
But I have same problem using gopro hero 4 & 5.

Hello Mika,

The software application, encoding settings, and the actual signal being output from your camera will have a huge influence on the behavior of your AV.io 4K unit. You can verify the signal being received by the AV.io 4K using the configuration tool as a reference. It is possible that your GoPro is outputting an incorrect signal for your desired UHD resolution.

We tested our GoPro Hero 6 in 4K resolution and initially received the same letter-boxing results with UHD resolutions in Open Broadcast Software Studio. In our configuration tool, the signal being seen by our AV.io 4K was 1280 X 720, at 60 FPS. Upon disconnecting and reconnecting the HDMI cable, and changing resolution settings on GoPro to a different resoltuon and back again to 4K, the signal output the correct 3840 X 2160 resolution at 30 FPS in the configuration tool.