If you have a dodgy source jar file, it will probably blow up the ensime server with java.util.zip.ZipException: error in opening zip file. The solution offered in the project’s Github issue is to delete your local copy of the bad file and add it to the list of excluded classifiers in ivy (i.e. ~/.ivy2/exclude_classifiers), and report the file to the nexus hosts to have it deleted.

Mine is a bit longer …