Invalid access to memory - System::TObject::ClassName

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 5.21.5

Error message:
Invalid access to memory.

Stack trace:
(0043BB7F) System::TObject::ClassName
(00097AFF) ntdll.dll
(00076021) ntdll.dll.KiUserExceptionDispatcher
(002463A4) Vcl::Forms::TApplication::HandleException
(003C9C0C) System::Classes::_18201
(00046DD0) USER32.dll
(00026275) USER32.dll
(00024BA3) USER32.dll
(000246DB) USER32.dll.DispatchMessageW

(0043BDD4) System::TObject::Free
(00097AFF) ntdll.dll
(00076021) ntdll.dll.KiUserExceptionDispatcher
(003C9C0C) System::Classes::_18201
(00046DD0) USER32.dll
(00026275) USER32.dll
(00024BA3) USER32.dll
(000246DB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 6.6

Error message:
Copying files to remote side failed.

Invalid access to memory.

Stack trace:
(00165F18) System::TObject::ClassName
(005EDDC0) Jclhookexcept::_16406
(005EDFA9) Jclhookexcept::_16409
(00C754DA) ____ExceptionHandler
(000B3490) ntdll.dll
(000B345F) ntdll.dll
(0006DD2E) ntdll.dll
(0007A7CA) ntdll.dll.KiUserExceptionDispatcher
(0015D483) System::UnicodeString::UnicodeString
(0091585A) ExceptionLogString
(0015D343) System::UnicodeString::~UnicodeString
(00A8EBE5) TSessionLog::AddException
(00C5D0C8) ___VCL_add_EH
(00A014CC) TSCPFileSystem::CopyToRemote
(0039A9DA) System::Internal::Strhlpr::UnicodeAppend
(00164A8C) System::FreeMem
(00167EE8) System::UStrClr
(0039AA41) System::Internal::Strhlpr::UnicodeFree
(0015D343) System::UnicodeString::~UnicodeString
(00164A70) System::GetMem
(0015D343) System::UnicodeString::~UnicodeString
(009509D4) TCopyParamType::GetLogStr
(0039AA41) System::Internal::Strhlpr::UnicodeFree
(00AFE122) TTerminal::LogTotalTransferDetails
(00AFA82B) TTerminal::CopyToRemote
(00154663) KERNELBASE.dll
(00C5CE5D) __internal_malloc
(00C55189) operator new
(0039AA41) System::Internal::Strhlpr::UnicodeFree
(0039AA32) System::Internal::Strhlpr::UnicodeAssign
(0015D3B1) System::UnicodeString::UnicodeString
(00ADB319) TTerminal::SetCurrentDirectoryW
(009B9B43) TUploadQueueItem::DoTransferExecute
(009B885F) TTransferQueueItem::DoExecute
(002E93FF) System::Syncobjs::TCriticalSection::Release
(009B6BA9) TQueueItem::Execute
(009B66D0) TTerminalItem::ProcessEvent
(000781BA) ntdll.dll.ZwWaitForSingleObject
(001556F2) KERNELBASE.dll.WaitForSingleObjectEx
(00155710) KERNELBASE.dll.WaitForSingleObjectEx
(0015565D) KERNELBASE.dll.WaitForSingleObject
(009B245A) TSignalThread::WaitForEvent
(009B24D4) TSignalThread::Execute
(009B1EDF) TSimpleThread::ThreadProc
(000FDD8C) C20_0
(00167D7C) System::_17354
(00014D47) KERNEL32.DLL.BaseThreadInitThunk
(0006C839) ntdll.dll
(0006C7BC) ntdll.dll

I know how to reproduce the problem or the problem happens frequently enough. I wish to be contacted by the WinSCP team to help resolving the problem.