ClassLoaderExt::check is only called for the boot loader. The signed JAR file checking should be remove from ClassLoaderExt::check:

bool ClassLoaderExt::check(ClassLoaderExt::Context *context,
                          const ClassFileStream* stream,
                          const int classpath_index) {
 if (stream != NULL) {
- // Ignore any App classes from signed JAR file during CDS archiving
- // dumping
- if (DumpSharedSpaces &&
- SharedClassUtil::is_classpath_entry_signed(classpath_index) &&
- classpath_index >= _app_paths_start_index) {
- tty->print_cr("Preload Warning: Skipping %s from signed JAR",
- context->class_name());
- return false;
- }