Jetty 12 with Scala "Unable to locate class corresponding to inner class entry for Scope"

Question

After upgrading jetty-server from 11 to 12, the compilation (using mill as the build tool) fails with:

Unable to locate class corresponding to inner class entry for Scope in owner org.eclipse.jetty.server.UserIdentity

But nowhere in my servlet code this UserIdentity class is used.

What might this error message mean and how to fix it?

My full list of dependencies (with versions that still worked):

  def ivyDeps = Agg( // https://search.maven.org
    ivy"org.apache.kafka::kafka-streams-scala::2.8.2",
    ivy"org.eclipse.jetty:jetty-server:11.0.2",
    ivy"org.eclipse.jetty.websocket:websocket-jetty-server:11.0.22",
    ivy"org.json4s::json4s-jackson::4.0.7",
    ivy"org.scala-lang.modules::scala-parallel-collections::1.0.4",
    ivy"org.slf4j:slf4j-api:2.0.13",
    ivy"org.slf4j:slf4j-simple:2.0.13",
    ivy"com.github.scopt::scopt::4.1.0"
  )