This issue is being tracked already:
https://winscp.net/tracker/1684

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.

I'm connected to a ftp (with SSH key) trough a VPN server.
If I disconnect from VPN without quitting WinSCP, it asks for a password. I click on X to cancel and then, the invalid memory access error shows up. I need to manually End task in Windows task manager.

Thanks

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WinSCP 5.13.5

Error message:
Accès mémoire invalide.

Trace de la pile :
(003F2A9F) System::DoneExcept
(00083FFF) ntdll.dll
(00071931) ntdll.dll.KiUserExceptionDispatcher
(00380EE0) System::Classes::_18201
(00045359) USER32.dll
(00036297) USER32.dll
(000353D6) USER32.dll
(000351AB) USER32.dll.DispatchMessageW

(003F268C) System::HandleAnyException
(00083FFF) ntdll.dll
(00071931) ntdll.dll.KiUserExceptionDispatcher
(00380EE0) System::Classes::_18201
(00045359) USER32.dll
(00036297) USER32.dll
(000353D6) USER32.dll
(000351AB) USER32.dll.DispatchMessageW

Status: all_insignificant

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.