<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 5.17.6

Error message:
External exception C0000006

Stack trace:
(0000EB50) MPR.DLL.WNetGetUniversalNameW
(00087E3F) ntdll.dll
(000732D1) ntdll.dll.KiUserExceptionDispatcher
(003F2C52) System::Sysutils::ExpandUNCFileName
(00DA763E) TTerminal::Source
(00DA6472) TTerminal::SourceRobust
(00DA62B1) TTerminal::DoCopyToRemote
(00D74056) TSFTPFileSystem::CopyToRemote
(00DA5D05) TTerminal::CopyToRemote
(0000FC56) TCustomScpExplorerForm::ExecuteCopyMoveFileOperation
(00010848) TCustomScpExplorerForm::ExecuteFileOperation
(0002461D) TCustomScpExplorerForm::RemoteFileControlDragDropFileOperation
(000247B5) TCustomScpExplorerForm::RemoteFileControlDDFileOperation
(00C3BF46) TUnixDirView::PerformItemDragDropOperation
(00446DD0) Customdirview::TCustomDirView::DDProcessDropped
(0047BEB7) Dragdrop::TDragDrop::WndMethod
(003A4AC8) System::Classes::_18201
(000434B9) USER32.dll
(00023FF7) USER32.dll
(00023149) USER32.dll
(00022F2B) 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 5.13.3

Error message:
External exception C000001D

Stack trace:
(0000ED23) MPR.DLL.WNetGetUniversalNameW
(0007DA8F) ntdll.dll
(0006B6B1) ntdll.dll.KiUserExceptionDispatcher
(003CC934) System::Sysutils::_16875
(003CCC1A) System::Sysutils::ExpandUNCFileName
(007A868F) TSFTPFileSystem::Sink
(007D2623) TTerminal::Sink
(007D1666) TTerminal::SinkRobust
(007D14B4) TTerminal::DoCopyToLocal
(007A6E26) TSFTPFileSystem::CopyToLocal
(007D0FDE) TTerminal::CopyToLocal
(000120D7) TCustomScpExplorerForm::TemporarilyDownloadFiles
(00012CF9) TCustomScpExplorerForm::ExecuteFile
(000132DE) TCustomScpExplorerForm::ExecuteFile
(00018B04) TCustomScpExplorerForm::DoDirViewExecFile
(000189AA) TCustomScpExplorerForm::DirViewExecFile
(0041FE98) Customdirview::TCustomDirView::Execute
(0041D89E) Customdirview::TCustomDirView::DoExecute
(0041E46F) Customdirview::TCustomDirView::WMLButtonDblClk
(0025B025) Vcl::Controls::TWinControl::WndProc
(0029EF53) Vcl::Comctrls::TCustomListView::WndProc
(00380370) System::Classes::_18201
(0003AE69) USER32.dll
(00037335) USER32.dll
(00016AF8) USER32.dll.CallWindowProcW
(00049AD7) COMCTL32.DLL
(00049B76) COMCTL32.DLL
(00049930) COMCTL32.DLL
(0003AE69) USER32.dll
(00037335) USER32.dll
(00016AF8) USER32.dll.CallWindowProcW
(00443213) Dragdrop::TDragDrop::WndMethod
(00380370) System::Classes::_18201
(0003AE69) USER32.dll
(00037335) USER32.dll
(00036BE9) USER32.dll
(000369CB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.