I'd like to confirm that you have a larger size of the thumbnail available for Hub to access. Unfortunately, I cannot do this for you because it requires an authentication token, but if you could kindly verify it for me:
1. Go to https://cityofsydney.maps.arcgis.com/home/item.html?id=295675f834174b08bb8d4ea2af5e0d42
2. Right-click your thumbnail image and select "open image in new tab"
![KlaraSchmitt_0-1638396412923.png KlaraSchmitt_0-1638396412923.png](https://community.esri.com/t5/image/serverpage/image-id/28660i41559A05116E7988/image-size/medium?v=v2&px=400)
3. In that new tab, go up to the browser URL bar and at the very end of everything typed in there (it might be really long with your access token), add &w=400 to the end. No spaces. Just insert your cursor at the end of the URL, type in &w=400 and press enter.
If you have a larger image associated with the Item, it will be displayed, and if so, please let me know (or you can take a screenshot and post it here.) If you still see a small thumbnail (200x133), then I do recommend you follow Amanda Bishop's suggestion and re-upload a larger image because for whatever reason the larger version hasn't been attached correctly.