(This is reflected in cljs.spec-test/test-roundtrip failing in Nashorn under Java 9.)
Node, when running these tests, in addition to cleaning up .cljs_nashorn_repl/ it is important to clean up nashorn_code_cache/ in order to ensure reproducibility.
Under Java 9, the first s/conform fails, but the second succeeds.
Printing *e which is actually a Java exception seems to indicate that it is an internal error:
java version "9.0.4"
Java(TM) SE Runtime Environment (build 9.0.4+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)