Rich Text field is producing weird space character instead of &nbsp;
I did contact Craft about this near the time this question was posted, they were not sure why it was occuring.

I found that this issue was environment specific, it was specifically happening locally on MAMP4, with 5.6.* using NGINX.

I was unable to find the cause of the issue, but, in the end it was not happening on server environments so I decided to give up.