I was seeing a similar issue. The Groovy Console stopped working and gave me the following error.
GET /apps/groovyconsole.html HTTP/1.1] org.apache.sling.servlets.get.impl.DefaultGetServlet No renderer for extension html
Restarting AEM resolved the issue. But the Console started behaving erratically (script edit window not loading) after I visited the /apps/archetype13/config node in CRXDE. I noticed that even though I didn't make any changes to this node in CRXDE, after I load /apps/archetype13/config/org.apache.sling.commons.log.LogManager.factory.config-archetype13.config (by double-clicking on it) when I try to navigate away from CRXDE I get the question "Leave site? (Changes you made may not be saved.)". Even though I made no changes. After this the erratic behavior starts.
As someone stated above, it's as if the resourceType resolution is failing and the request is reaching DefaultGetServlet. But not sure why that is happening.
My issue seems to have resolved itself after building with Oracle JDK 8 and running AEM with Oracle JDK 11. Previously I was building and running with OpenJDK because I couldn't find a way to install Oracle JDKs via Homebrew. So I gave in and used the Oracle installers. (Note: I use bash profile aliases to switch between Java versions. And somehow running AEM on Oracle JDK 8 causes issues, so I'm using Oracle JDK 11.)