External exception EEFFACE - TFTPFileSystem::DoWaitForReply

<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 5.7.6

Error message:
External exception EEFFACE

Stack trace:
(000D1ED2) KERNELBASE.dll.RaiseException
(000A267F) ntdll.dll
(0009018A) ntdll.dll.KiUserExceptionDispatcher
(0049641C) Jclhookexcept::_16408
(007E4F0E) C4799_3
(007E62FF) _ReThrowException
(00659E58) TFTPFileSystem::DoWaitForReply
(00659ED7) TFTPFileSystem::WaitForReply
(00659F30) TFTPFileSystem::WaitForCommandReply
(006546D8) TFTPFileSystem::Source
(00653DA2) TFTPFileSystem::SourceRobust
(00653B98) TFTPFileSystem::CopyToRemote
(00723225) TTerminal::CopyToRemote
(0000C302) TCustomScpExplorerForm::ExecuteFileOperation
(0001D2A9) TCustomScpExplorerForm::RemoteFileControlDragDropFileOperation
(0001D432) TCustomScpExplorerForm::RemoteFileControlDDFileOperation
(0061488A) TUnixDirView::PerformItemDragDropOperation
(003D969E) Customdirview::TCustomDirView::DDProcessDropped
(003FEF8B) Dragdrop::TDragDrop::WndMethod
(003402A8) System::Classes::_18201
(00034B81) USER32.dll
(00018D15) USER32.dll
(0001885B) USER32.dll
(000186AB) USER32.dll.DispatchMessageW

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.

Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.

This happens when I attempt to transfer a very large number of files. The transfer proceeds for a long time, but after a day or so WinSCP will crash like this. it's possible that long pathnames are a factor as well, but I'm unsure. This is occurring on Windows Server 2016 Datacenter.

WinSCP 6.5.5

Error message:
External exception EEFFACE

Stack trace:
(000DC692) KERNELBASE.dll.RaiseException
(000826CF) ntdll.dll
(0007022A) ntdll.dll.KiUserExceptionDispatcher
(005CABA0) Jclhookexcept::_16410
(00EF7D16)
(00EF9107)
(00C1B178) TFTPFileSystem::DoWaitForReply
(00C1B1F7) TFTPFileSystem::WaitForReply
(00C1B250) TFTPFileSystem::WaitForCommandReply
(00C130E9) TFTPFileSystem::Sink
(00D552B6) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTerminal::ProcessDirectory
(00D54974) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTerminal::ProcessDirectory
(00D54974) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTerminal::ProcessDirectory
(00D54974) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTerminal::ProcessDirectory
(00D54974) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTerminal::ProcessDirectory
(00D54974) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTerminal::ProcessDirectory
(00D54974) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTerminal::ProcessDirectory
(00D54974) TTerminal::Sink
(00D53FB4) TTerminal::SinkRobust
(00D55883) TTerminal::SinkFile
(00D3CF8B) TTermin

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.