<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 5.11.3

Error message:
Copie de fichiers vers le coté distant échouée.

Accès mémoire invalide.

Trace de la pile :
(000FE8A8)
(0089D34A) C5067_0
(0089F3B2) ____ExceptionHandler
(0089C16C) __ExceptionHandler
(0005A646) ntdll.dll
(0000F10A) ntdll.dll.KiUserExceptionDispatcher
(007B02EC) TTerminal::CopyToRemote
(006E20BC) TUploadQueueItem::DoTransferExecute
(006E0D9A) TQueueItem::Execute
(006DFDD2) TTerminalItem::ProcessEvent
(006DE17C) TSignalThread::Execute
(000A0DD7) Userinterface::C20_0
(00012675) kernel32.dll.BaseThreadInitThunk
(00038F40) ntdll.dll
(00038F10) ntdll.dll

The problem happens rarely. I cannot reproduce it.