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)>

Just after we were access to our contents with FTP and googled something for a while, I realized that this incident occurred.
Furthermore, we found this type of problems not a few times only when we connecting some specific contents.

WinSCP 5.15.9

Error message:
メモリのアクセス違反

スタック トレース:
(0021AB5C) Vcl::Graphics::TBrush::SetColor
(00087D6F) ntdll.dll
(00073211) ntdll.dll.KiUserExceptionDispatcher
(002746D5) Vcl::Controls::TControl::WndProc
(00274310) Vcl::Controls::TControl::Perform
(002796C2) Vcl::Controls::TWinControl::PaintControls
(002794C1) Vcl::Controls::TWinControl::PaintHandler
(00279BD0) Vcl::Controls::TWinControl::WMPaint
(0027EFA9) Vcl::Controls::TCustomControl::WMPaint
(00279219) Vcl::Controls::TWinControl::WndProc
(00278860) Vcl::Controls::TWinControl::MainWndProc
(003A3E7C) System::Classes::_18201
(000438E9) USER32.dll
(00025137) USER32.dll
(00024CD5) USER32.dll
(0002D6BD) USER32.dll
(000731CB) ntdll.dll.KiUserCallbackDispatcher
(0002406B) USER32.dll.DispatchMessageW

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.