This is Lilliput JDK 17 specific, later versions have JDK-8278568 refactoring.

We have missed the `set_klass_gap(0)` line in the patch here:

```
    } else {
      assert(size == CollectedHeap::min_fill_size(),
             "size for smallest fake object doesn't match");
      instanceOop obj = (instanceOop) cast_to_oop(allocate(size));
- obj->set_mark(markWord::prototype());
- obj->set_klass_gap(0);
- obj->set_klass(vmClasses::Object_klass());
+ if (UseCompactObjectHeaders) {
+ obj->set_mark(vmClasses::Object_klass()->prototype_header());
+ } else {
+ obj->set_mark(markWord::prototype());
+ obj->set_klass(vmClasses::Object_klass());
+ }
    }
  }
```