<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 5.21.5

Error message:
Invalid access to memory.

Stack trace:
(0043BB7F) System::TObject::ClassName
(00097AFF) ntdll.dll
(00076021) ntdll.dll.KiUserExceptionDispatcher
(002463A4) Vcl::Forms::TApplication::HandleException
(003C9C0C) System::Classes::_18201
(00046DD0) USER32.dll
(00026275) USER32.dll
(00024BA3) USER32.dll
(000246DB) USER32.dll.DispatchMessageW

(0043BDD4) System::TObject::Free
(00097AFF) ntdll.dll
(00076021) ntdll.dll.KiUserExceptionDispatcher
(003C9C0C) System::Classes::_18201
(00046DD0) USER32.dll
(00026275) USER32.dll
(00024BA3) USER32.dll
(000246DB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.