<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 5.13.1

Error message:
External exception C0000006

Stack trace:
(0001F9F0) msIso.dll
(0007DA8F) ntdll.dll
(0006B6B1) ntdll.dll.KiUserExceptionDispatcher
(00131492) ieframe.dll
(0013136A) ieframe.dll
(00130035) ieframe.dll
(0012AF91) ieframe.dll
(00127526) ieframe.dll
(001291D5) ieframe.dll
(000C3DCF) ieframe.dll
(000C4B67) ieframe.dll
(000C51FC) ieframe.dll
(000C73E8) ieframe.dll
(004F6F4B) Shdocvw::TWebBrowser::Navigate
(000742FD) TBrowserViewer::NavigateToUrl
(00074628) NavigateBrowserToUrl
(00823BFA) TMessageForm::LoadMessageBrowser
(00217AFD) Vcl::Forms::TCustomForm::CMShowingChanged
(00823B50) TMessageForm::CMShowingChanged
(00259A15) Vcl::Controls::TWinControl::WndProc
(00213EDC) Vcl::Forms::TCustomForm::WndProc
(00858868) Vclcommon::C2785_0

The problem happens rarely. I cannot reproduce it.