See screenshot.

Might be related to the way the new ametys home feature have been implemented.
See resource-exists and is-cacheable action of the site sitemap.
It seems to only affect images.

If you do not have a configured apache in front of tomcat, image will always be not found. If you do, image will be found as soon as they are in the apache frontal cache (after reloading the page a second time for example).