This bug has been added to the tracker:
https://winscp.net/tracker/1510

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 5.9.3

Error message:
Invalid access to memory.

Stack trace:
(00718918) TSessionData::GetUsesSsh
(00081D3F) ntdll.dll
(0006F8EA) ntdll.dll.KiUserExceptionDispatcher
(007C92A2) TGenerateUrlDialog::Execute
(007C04CF) DoGenerateTransferCodeDialog
(007A50B6) TCopyDialog::GenerateCode
(007A516E) TCopyDialog::CopyParamClick
(0044A0D7) Tb2item::TTBCustomItem::Click
(00373100) System::Classes::_18201
(0002C2B1) USER32.dll
(0000D885) USER32.dll
(0000D1DF) USER32.dll
(0000CF9B) 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.