O i was of the understanding you shot at a lower RES, if you want to shoot 4K60 and you cant that suck for sure.
In the Sj7 i find that some memory cards just will not work it with the more demanding recordings, wich is funny cuz its memory cards with a write speed 3-4 X faster than the Sj7 will ever write with even using the most high settings.
Is it just 4K/60 that are a problem for you, and how about if you use lowest image quality / bitrate ?
Not that you should be forced to do so, i only use highest settings myself on anything, but it might give a hint that the culprit might be the memory card and not the camera. ( not sure if SJcams have formulated a memory card to use list for the Sj8 yet )
Too bad you are all the way over there in Northamerican "Denmark", or i would have a couple of U3 cards you could give a try to see if they work better than what you have,