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 5.15.4

Error message:
メモリのアクセス違反

スタック トレース:
(004184D0) System::UStrAsg
(00087E3F) ntdll.dll
(000732C1) ntdll.dll.KiUserExceptionDispatcher
(00085338) TFrameAnimation::CalculateNextFrameTick
(000852E8) TFrameAnimation::Animate
(003A3E28) System::Classes::_18201
(00043449) USER32.dll
(00023F87) USER32.dll
(000230D9) USER32.dll
(00022EBB) 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.