<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 5.9.2

Error message:
External exception EEFFACE

Трассировка стека:
(000D96F2) KERNELBASE.dll.RaiseException
(0008148F) ntdll.dll
(0006F02A) ntdll.dll.KiUserExceptionDispatcher
(004B8B7C) Jclhookexcept::_16408
(0086409A) C5073_3
(0086548B) _ReThrowException
(00014F50) TCustomScpExplorerForm::CalculateSize
(007F77F0) TPropertiesDialog::CalculateSizeButtonClick
(0024A63B) Vcl::Controls::TControl::Click
(0024EC29) Vcl::Controls::TWinControl::WndProc
(001B6DA0) Vcl::Stdctrls::TButtonControl::WndProc
(0024ED8F) Vcl::Controls::_17076
(0024EC29) Vcl::Controls::TWinControl::WndProc
(0024E270) Vcl::Controls::TWinControl::MainWndProc
(00372BEC) System::Classes::_18201
(0002C2B1) USER32.dll
(0000D885) USER32.dll
(0000D4BB) USER32.dll
(00017B07) USER32.dll
(0006F004) ntdll.dll.KiUserCallbackDispatcher
(0000FBFB) USER32.dll.SendMessageW
(0004C369) COMCTL32.DLL
(0005C060) COMCTL32.DLL
(0002C2B1) USER32.dll
(0000D885) USER32.dll
(0000CF12) USER32.dll.CallWindowProcW
(0024ED3A) Vcl::Controls::TWinControl::DefaultHandler
(0024EC29) Vcl::Controls::TWinControl::WndProc
(001B6DA0) Vcl::Stdctrls::TButtonControl::WndProc
(00372BEC) System::Classes::_18201
(0002C2B1) USER32.dll
(0000D885) USER32.dll
(0000D1DF) USER32.dll
(0000CF9B) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.

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

<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 5.7.3

Error message:
External exception EEFFACE

Stack trace:
(0000B41F) KERNELBASE.dll.RaiseException
(0005A466) ntdll.dll
(0000F12E) ntdll.dll.KiUserExceptionDispatcher
(00495FDC) Jclhookexcept::_16408
(007E24F6) C4799_3
(007E38E7) _ReThrowException
(0001315C) TCustomScpExplorerForm::CalculateSize
(00779A38) TPropertiesDialog::CalculateSizeButtonClick
(00217907) Vcl::Controls::TControl::Click
(0021BEF5) Vcl::Controls::TWinControl::WndProc
(00184960) Vcl::Stdctrls::TButtonControl::WndProc
(0021C05B) Vcl::Controls::_17076
(0021BEF5) Vcl::Controls::TWinControl::WndProc
(0021B53C) Vcl::Controls::TWinControl::MainWndProc
(0033FE18) System::Classes::_18201
(000152F7) USER32.dll
(00015D35) USER32.dll
(00015DE3) USER32.dll
(00015E41) USER32.dll
(0000F107) ntdll.dll.KiUserCallbackDispatcher
(000186C0) USER32.dll.SendMessageW
(000A35FB) COMCTL32.DLL
(000A365E) COMCTL32.DLL
(000A34E8) COMCTL32.DLL
(000152F7) USER32.dll
(00015D35) USER32.dll
(0001FD22) USER32.dll
(0001FD48) USER32.dll.CallWindowProcW
(0021C006) Vcl::Controls::TWinControl::DefaultHandler
(0021BEF5) Vcl::Controls::TWinControl::WndProc
(00184960) Vcl::Stdctrls::TButtonControl::WndProc
(0033FE18) System::Classes::_18201
(000152F7) USER32.dll
(00015D35) USER32.dll
(000167BF) USER32.dll
(00016885) USER32.dll.DispatchMessageW