Zugriffsverletzung - ungültiger Zugriff auf den Speicher - System::IsClass

<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 5.11.2

Error message:
Zugriffsverletzung - ungültiger Zugriff auf den Speicher.

Stack trace:
(003EC550) System::IsClass
(000851DF) ntdll.dll
(00073161) ntdll.dll.KiUserExceptionDispatcher
(0041BE0F) Customdirview::TCustomDirView::RestoreState
(00005A84) TCustomScpExplorerForm::SetTerminal
(00096291) TTerminalManager::TerminalReady
(00093AE6) TTerminalManager::SetActiveTerminal
(0001C5F4) TCustomScpExplorerForm::SessionsPageControlChange
(00257C85) Vcl::Controls::TWinControl::WndProc
(00252D7C) Vcl::Controls::TControl::Perform
(00257DEB) Vcl::Controls::_17076
(00257C85) Vcl::Controls::TWinControl::WndProc
(0021214C) Vcl::Forms::TCustomForm::WndProc

The problem happens rarely. I cannot reproduce it.

I had just clicked on "upload" to upload 2 selected files.
Usually works fine.
System under load at the time.

Note - I click on upload nowadays because right click on file does not always work.
Sometimes it brings up the menu on right click but then hangs and I have to force close WinSCP.

WinSCP 6.1.2

Error message:
External exception C0000006

Stack trace:
(00293CBC) System::IsClass
(0008792F) ntdll.dll
(00073F81) ntdll.dll.KiUserExceptionDispatcher
(003B6129) Vcl::Forms::TCustomForm::IsShortCut
(003F8F88) Vcl::Controls::TWinControl::IsMenuKey

The problem happens rarely. I cannot reproduce it.