It's a well known artifact with sony cameras. Referred to mostly as 'highlight aliasing'. Google 'highlight aliasing' and you will find many hits. It is a lot more egregious in HD than it is in 4k but its clearly still there. Aparently It was even apparent on the f5 and f55 but was addressed and removed on those cameras. On other cameras like the fs700 it wasn't addressed. However, people observed with the fs700 that it could be bypassed with Raw recording. Go and look at videos shot with sony cameras. Now that you have seen it you will notice it everywhere! Even in cases were you can't see it obviously it still alters the overal look of the image as a whole, making it seem over sharp and less organic. Its a big contributor to sonys reputation as giving a video look. The good news for you is that it is smaller in 4k and in most cases people wont notice it.
Great if you forgot your tripod, but try any deliberate movement and you get some nasty digital jitter. My wife doesn't know cameras and even she went "ew" when she looked at it.
Kind of disappointing. Good effort, but limited usage