<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 5.19.2

Error message:
External exception EEFFACE

Stack trace:
(0012A512) KERNELBASE.dll.RaiseException
(0008788F) ntdll.dll
(00073EC1) ntdll.dll.KiUserExceptionDispatcher
(00531F00) Jclhookexcept::_16408
(00FBCE66) C5294_3
(00FBE257) _ReThrowException
(00E695D2) TSynchronizeDialog::Start
(00E693F5) TSynchronizeDialog::StartButtonClick
(00280255) Vcl::Controls::TWinControl::WndProc
(001E83E4) Vcl::Stdctrls::TButtonControl::WndProc
(002803BB) Vcl::Controls::_17076
(00280255) Vcl::Controls::TWinControl::WndProc
(0023A71C) Vcl::Forms::TCustomForm::WndProc

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 the 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 5.17.9

Error message:
External exception EEFFACE

Stack trace:
(001136D2) KERNELBASE.dll.RaiseException
(00088F9F) ntdll.dll
(000741F1) ntdll.dll.KiUserExceptionDispatcher
(00510438) Jclhookexcept::_16408
(00F8A786) C5296_0
(00F8BB77) _ReThrowException
(00E370F2) TSynchronizeDialog::Start
(00E36F15) TSynchronizeDialog::StartButtonClick
(0027ACF1) Vcl::Controls::TWinControl::WndProc
(001E2E80) Vcl::Stdctrls::TButtonControl::WndProc
(0027AE57) Vcl::Controls::_17076
(0027ACF1) Vcl::Controls::TWinControl::WndProc
(002351B8) Vcl::Forms::TCustomForm::WndProc

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.