Hey,
So the YouTube video is no longer available. However, I do have a simular issue with ny 50-140 lens at 140mm. In Manual focus, during video recording, it seems the focus is sort of pulsing at times which can ruin that part of a video. I am not sure what causes the issue but, I have reached out to Fuji in hopes they can help. I will try to remember to update here if/when I hear back!
Did you by chance solve you issue @jufoso?