Hi, I have the same problem. I downloaded your video and it stutters on my Macbook Pro 15" Retina mid 2012. I use Quicktime player and iMovie sam result. I have the latest macOS Mojave which supports HVEC video format and my 4K video from iPhone 7 has no issues with playback or my Hero 5 4K video.
I just downloaded the file on my 2017 MacBook with 16gb of Ram. I opened it with IINA player and QuikTime Player. The file played perfectly on both for me. It doesn't seem like the GoPro is the problem. I don't know what to tell you.
I am experiencing the exact same issue as you and I built my pc from ground up with a dedicated graphics card etc... Our rigs are strong enough and capable enough to run these videos as they appear on the GoPro itself (smooth). The only idea I have is both our devices (my other being an early MacBook pro-2015 13in) do not support HEVC video encoding and because of that, the videos run very choppy.
Just as you described mine runs great for the first 1-2 seconds then choppy then back to normal and then choppy once again.
