Managed to sort some of it.
I can now edit the page from the front end, needed to turn off Compress Javascript Files in Helix Ultimate template.
The image issues still remain, have just noticed that the element background image is missing as well as the wrongly positioned image. Oddly, when I edit the page from the front end the images are present and in the correct position.
https://imgur.com/a/6JfuYO4
Top image is during edit, second is when editor closed.
The number of errors has now reduced to 2 similar errors in the web inspector.
Unchecked runtime.lastError: The message port closed before a response was received. https://www.mysite.org9/:1
Any ideas?