I managed to figure this out by playing around but it’s a bit disappointing that I could find no solutions online. There were a lot of people reporting the issue but with no response.
The images were included in another post which was set to “draft” this for some reason put the images into some kind of hidden state and although I could add them to the gallery and view them when logged in as admin, the links didn’t work.
It would probably be better if there was a publish status in the media list to show the status of images etc. if that had been the case I would have spotted the issue early on.