Since 14.6.3, component icons in the Channel Manager are rendered with fully qualified URLs instead of relative URLs. This seems unintended and causes problems in case the CMS host is different than the site host.
In org.hippoecm.hst.pagecomposer.jaxrs.model.ComponentRepresentation#represent there's this piece of code
Note, the last "false" is a fullyQualified flag.
On a local 14.6.2 archetype-based project, this is a relative URL, e.g.
On a local 14.6.3 archetype-based project, this is a fully qualified URL, e.g.
CMS-14805 to be the cause.