We have similar problem:
02.05.2016 16:22:29.536 *ERROR* [172.18.138.10 [1462198941448] GET /content/bla/bla/de.html HTTP/1.1] org.apache.sling.servlets.get.impl.DefaultGetServlet No renderer for extension html, cannot render resource JcrNodeResource, type=nt:unstructured, superType=null, path=/content/bla/bla/de/jcr:content/footer/morelinks/link_0_copy
We checked Apache Sling Resource Resolver Factory and found exactly the 4 entries mentioned above in the Resource Search Path.
More recommendations, how to solve this problem?