<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 6.1.1

Error message:
Unzulässiger Zugriff auf einen Speicherbereich.

Stapelverfolgung:
(00DEB8BE) TSFTPFileSystem::Sink
(0100350E) C6083_0
(01005576) ____ExceptionHandler
(01002330) __ExceptionHandler
(0008792F) ntdll.dll
(00073F81) ntdll.dll.KiUserExceptionDispatcher
(00E17840) TTerminal::DoCopyToLocal
(00DE79A2) TSFTPFileSystem::CopyToLocal
(00E14023) TTerminal::CopyToParallel
(00D1F257) TParallelTransferQueueItem::DoExecute
(00D1DBE6) TQueueItem::Execute
(00D1CC16) TTerminalItem::ProcessEvent
(00D1AF4C) TSignalThread::Execute
(000CD83B) Userinterface::C20_0
(0001ECC7) KERNEL32.DLL.BaseThreadInitThunk
(00066B1C) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00066AE9) ntdll.dll.RtlGetAppContainerNamedObjectPath

(00DEB8BE) TSFTPFileSystem::Sink
(0100350E) C6083_0
(01005576) ____ExceptionHandler
(01002330) __ExceptionHandler
(0008792F) ntdll.dll
(00073F81) ntdll.dll.KiUserExceptionDispatcher
(00E17840) TTerminal::DoCopyToLocal
(00DE79A2) TSFTPFileSystem::CopyToLocal
(00E14023) TTerminal::CopyToParallel
(00D1F257) TParallelTransferQueueItem::DoExecute
(00D1DBE6) TQueueItem::Execute
(00D1CC16) TTerminalItem::ProcessEvent
(00D1AF4C) TSignalThread::Execute
(000CD83B) Userinterface::C20_0
(0001ECC7) KERNEL32.DLL.BaseThreadInitThunk
(00066B1C) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00066AE9) ntdll.dll.RtlGetAppContainerNamedObjectPath

The problem happens rarely. I cannot reproduce it.