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.

It happens every time I unlock the computer after having locked it up for a while.
The "Abnormal program termination" windows could not be closed by clicking OK since it pop up immediately again, the only way to get rid of it is by killing the WinSCP process.

WinSCP 5.17.9

Error message:
Invalid access to memory.

Stack trace:
(0027DB0B) Vcl::Controls::TWinControl::HandleNeeded
(0006248E) ntdll.dll
(0000F15E) ntdll.dll.KiUserExceptionDispatcher
(00049B2B) TNonVisualDataModule::DoIdle
(00049AE8) TNonVisualDataModule::SessionIdleTimerTimer
(003A5954) System::Classes::_18201
(000152F7) USER32.dll
(00015D35) USER32.dll
(000167BF) USER32.dll
(00016885) USER32.dll.DispatchMessageW
(0003C8F8) USER32.dll
(0003CA57) USER32.dll
(0006E7CB) USER32.dll.SoftModalMessageBox
(0006EAA7) USER32.dll
(0006EBAA) USER32.dll.MessageBoxTimeoutW
(0006EC29) USER32.dll.MessageBoxTimeoutA
(0006ED7C) USER32.dll.MessageBoxExA
(0006EDC1) USER32.dll.MessageBoxA
(00F867BA) __ErrorMessage
(00F86C21) __do_abort
(00F86CA8) _abort
(00F8B069) C5296_0
(00F8B1AA) C5296_0
(00F8B9B6) C5296_0
(00F8ADEB) C5296_0
(00F8BDE1) ____ExceptionHandler
(00F88D54) __ExceptionHandler
(0006248E) ntdll.dll
(00F89EC2) ___doGlobalUnwind
(00F8C0AE) ____ExceptionHandler
(00F88D54) __ExceptionHandler
(0006248E) ntdll.dll
(0000F15E) ntdll.dll.KiUserExceptionDispatcher
(00510438) Jclhookexcept::_16408
(002797FC) Vcl::Controls::TWinControl::CreateWnd
(002BB44B) Vcl::Comctrls::TCustomListView::CreateWnd
(0042EBD6) Nortonlikelistview::TCustomNortonLikeListView::CreateWnd
(0042AD81) Ielistview::TCustomIEListView::CreateWnd
(002B9E51) Vcl::Comctrls::TListItems::BeginUpdate
(004447EE) Customdirview::TCustomDirView::ClearItems
(00C3E3C1) TUnixDirView::DoSetTerminal

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.