void MemDetailDiffReporter::diff_malloc_site(const MallocSite* early, const MallocSite* current) const {
  assert(early->flags() == current->flags(), "Must be the same memory type"); <<--- here
  
  diff_malloc_site(current->call_stack(), current->size(), current->count(),
    early->size(), early->count(), early->flags());
}


MallocSite* early:

0x00000252`ef653218
   +0x000 _call_stack : NativeCallStack
      +0x000 __VFN_table : 0x00000000`579fc640
      =00000000`58102340 EMPTY_STACK : NativeCallStack
      +0x008 _stack :
       [00] 0x00000000`56cf83dc "H???"
       [01] 0x00000000`57250b88 "???"
       [02] 0x00000000`56e9e871 "H???"
       [03] 0x00000000`56d77abc "H???"
      +0x028 _hash_value : 0x5bb5f291
   +0x030 e : MemoryCounter
      +0x000 _count : 0xc
      +0x008 _size : 0x4600
      +0x010 _peak_count : 0x1e
      +0x018 _peak_size : 0x5500
   +0x050 _flags : 7 ( mtInternal ) <<--

MallocSite* current:

   0x00000252`eabbade8
   +0x000 _call_stack : NativeCallStack
      +0x000 __VFN_table : 0x00000000`579fc640
      =00000000`58102340 EMPTY_STACK : NativeCallStack
      +0x008 _stack :
       [00] 0x00000000`56cf83dc "H???"
       [01] 0x00000000`57250b88 "???"
       [02] 0x00000000`56e9e871 "H???"
       [03] 0x00000000`56d77abc "H???"
      +0x028 _hash_value : 0x5bb5f291
   +0x030 e : MemoryCounter
      +0x000 _count : 1
      +0x008 _size : 0x400
      +0x010 _peak_count : 4
      +0x018 _peak_size : 0x2c200
   +0x050 _flags : 5 ( mtGC ) <----
   
   
MallocSite stack:

[00]
jvm!AllocateHeap+0x37 [d:\dev\jdk\sandboxes\jfr_open_source\open\src\hotspot\share\memory\allocation.inline.hpp @ 70]:
00000000`56cf83d7 e8a4659600 call jvm!NativeCallStack::NativeCallStack (00000000`5765e980)
00000000`56cf83dc 4889442420 mov qword ptr [rsp+20h],rax
[01]
jvm!GenericGrowableArray::raw_allocate+0xb3 [d:\dev\jdk\sandboxes\jfr_open_source\open\src\hotspot\share\utilities\growablearray.cpp @ 55]:
00000000`57250b83 e81878aaff call jvm!AllocateHeap (00000000`56cf83a0)
00000000`57250b88 eb18 jmp jvm!GenericGrowableArray::raw_allocate+0xd2 (00000000`57250ba2)
[02]
jvm!GrowableArray<void * __ptr64>::grow+0x5c [d:\dev\jdk\sandboxes\jfr_open_source\open\src\hotspot\share\utilities\growablearray.hpp @ 446]:
00000000`56e9e86c e85f223b00 call jvm!GenericGrowableArray::raw_allocate (00000000`57250ad0)
00000000`56e9e871 4889442438 mov qword ptr [rsp+38h],rax
[03]
jvm!GrowableArray<InlineTree * __ptr64>::append+0x37 [d:\dev\jdk\sandboxes\jfr_open_source\open\src\hotspot\share\utilities\growablearray.hpp @ 216]:
00000000`56d77ab7 e8546d1200 call jvm!GrowableArray<void * __ptr64>::grow (00000000`56e9e810)
00000000`56d77abc 488b442440 mov rax,qword ptr [rsp+40h]


So:

  assert(early->flags() == current->flags(), "Must be the same memory type");

==

assert( 7 ( mtInternal ) == 5 ( mtGC ) "Must be the same memory type");

Attaching a file with assert context. There exist a 17GB mdmp file on my local workstation. Issue appeared when running Kitchensink locally.