In mappedEnumLookup, a local map is created when enumMap.map is null, but it's never assigned to enumMap.map which assumedly is the intent:

    private static <T extends Enum<T>> int mappedEnumLookup(T value, MethodHandles.Lookup lookup, Class<T> enumClass, EnumDesc<?>[] labels, EnumMap enumMap) {
        if (enumMap.map == null) {
            T[] constants = SharedSecrets.getJavaLangAccess().getEnumConstantsShared(enumClass);
            int[] map = new int[constants.length];
            int ordinal = 0;

            for (T constant : constants) {
                map[ordinal] = labels.length;

                for (int i = 0; i < labels.length; i++) {
                    if (Objects.equals(labels[i].constantName(), constant.name())) {
                        map[ordinal] = i;
                        break;
                    }
                }

                ordinal++;
            }
        }
        return enumMap.map[value.ordinal()];
    }

Since the return statement would throw a NPE if this path was exercised it's unclear if this is covered by tests.