Invalid pointer operat����� - TTerminal::Open

I received this error during a large (series of 1Gb files) binary xfer. This occurred about 60MB into the 2nd of five files in the directory being transferred.
WinSCP 5.9

Error message:
Invalid pointer operat耀

Please help us improving WinSCP by reporting the error on WinSCP support forum.

Stack trace:
(008627D9) C5073_3
(00863DB3) _ReThrowException
(0076CB45) TTerminal::Open
(0076DE53) TTerminal::Reopen
(0076FA2D) TTerminal::QueryReopen
(0076A0B5) TRobustOperationLoop::TryReopen
(00757FF3) TSFTPFileSystem::SFTPSourceRobust
(0075ED4D) TSFTPFileSystem::SFTPDirectorySource
(007583FD) TSFTPFileSystem::SFTPSource
(00757FBC) TSFTPFileSystem::SFTPSourceRobust
(0075714A) TSFTPFileSystem::CopyToRemote
(007837C5) TTerminal::CopyToRemote
(0000DCE5) TCustomScpExplorerForm::ExecuteFileOperation
(0000E9E4) TCustomScpExplorerForm::ExecuteFileOperation
(0000EA6B) TCustomScpExplorerForm::ExecuteFileOperationCommand
(0000EBF2) TCustomScpExplorerForm::ExecuteCopyOperationCommand
(000372C8) TNonVisualDataModule::ExplorerActionsExecute
(003B4768) System::Actions::TContainedActionList::ExecuteAction
(0019B96D) Vcl::Actnlist::TCustomAction::Execute
(0037264C) System::Classes::_18201
(000374F1) USER32.dll
(00015C3B) USER32.dll
(0001553C) USER32.dll
(000152FB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.