<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 5.21.6

Error message:
Invalid access to memory.

Stack trace:
(00D8779E) TSessionData::SetFtpAccount
(00FDF74E) C5412_0
(00FE17B6) ____ExceptionHandler
(00FDE570) __ExceptionHandler
(00087B7F) ntdll.dll
(00074001) ntdll.dll.KiUserExceptionDispatcher
(00D58947) TSessionData::DefaultSettings
(00D58AED) TSessionData::Default
(00D57791) TSessionData::TSessionData
(00D88A20) TStoredSessionList::TStoredSessionList
(00CB347A) CoreLoad
(00CB359B) CoreInitialize
(00FDD761) __wstartup
(00066BBC) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00066B89) ntdll.dll.RtlGetAppContainerNamedObjectPath

The problem happens rarely. I cannot reproduce it.