Thank you very much, Matt.
I had been researching google relating to aliasing which is what i figured it was, but adding "highlight" helped me find what I was looking for.
(This footage was 4K btw)
I've never heard of it until now. It is a bit of a concern to look at, but i've never noticed it on any sony footage until I was pixel peeping my own a6300, so I guess it won't be an issue to my clients either.
Hopefully a firmware update helps with it, but I won't hold my breath.