Can be easily reproduced with:

$ ./build/macosx-x86_64-normal-server-release/images/jdk/bin/java -XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI -XX:+UseJVMCICompiler --validate-modules
Uncaught exception at /Users/cthalinger/jdk10/hs/hotspot/src/share/vm/jvmci/jvmciCompiler.cpp:137
java.lang.NoClassDefFoundError: jdk/vm/ci/runtime/JVMCI

This happens when the first tier 4 compilation is scheduled:

$ ./build/macosx-x86_64-normal-server-release/images/jdk/bin/java -XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI -XX:+UseJVMCICompiler -XX:+PrintCompilation --validate-modules
...
     83 110 3 java.lang.invoke.MemberName::testFlags (16 bytes)
     83 111 3 java.lang.String::<init> (15 bytes)
     83 112 4 java.lang.String::hashCode (49 bytes)
Uncaught exception at /Users/cthalinger/jdk10/hs/hotspot/src/share/vm/jvmci/jvmciCompiler.cpp:137
java.lang.NoClassDefFoundError: jdk/vm/ci/runtime/JVMCI