GraalVM Javascript requires the use of Java.type(typename). It does not support accessing classes just by their fully qualified class name by default. Java.type brings more clarity and avoids the accidental use of Java classes in JavaScript code.

From the Nashorn Migration Guide.

I got ScriptCraft working on GraalVM by requesting the engine as "nashorn", which either returned the old engine, or a GraalVM engine in compatibility mode.

I'm using raw java class access in GraalVM and passing it back up to java for event handling in RepComm/RepCraft without a hitch.
Maybe they've changed how it works in the past months?