Hi Thomas, thanks for your reply
I still can't work it out!
I've set an image thumbnail in ArcGIS online on the item page. I cant see a metadata item here on the AGOL item for thumbnail.
When I check ArcGIS online assistant there is a line with thumbnail with the correct url to the thumbnail.
In Hubs metadata editor I can see all my items but I cant see the Site/Pages.
Also - looks like the arcgis URL for the site uses my header logo but the custom domain version doesnt load any image.