@pawel.mirgos: 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 was connected through ssh to my remote linux host, and clicked button "refresh" - error. Clicking key combination Ctrl+R worked,

WinSCP 5.21.6

Error message:
Nieprawidłowy dostęp do pamięci.

Stack trace:
(0003DC1C) USER32.dll
(00087B7F) ntdll.dll
(00074001) ntdll.dll.KiUserExceptionDispatcher
(0003AE40) USER32.dll.PeekMessageW
(004C7132) Tb2item::TTBModalHandler::Loop
(004C6113) Tb2item::TTBView::EnterToolbarLoop
(004D3C32) Tb2toolbar::TTBToolbarView::EnterToolbarLoop
(0027DF90) Vcl::Controls::TControl::DoMouseDown
(0027DFDF) Vcl::Controls::TControl::WMLButtonDown
(00282491) Vcl::Controls::TWinControl::WndProc
(00281AD8) Vcl::Controls::TWinControl::MainWndProc
(003C9C14) System::Classes::_18201
(00040489) USER32.dll
(00037445) USER32.dll
(000351B5) USER32.dll
(00034F7B) USER32.dll.DispatchMessageW

(0003B015) USER32.dll.PeekMessageW
(00087B7F) ntdll.dll
(00074001) ntdll.dll.KiUserExceptionDispatcher
(0003AE40) USER32.dll.PeekMessageW
(004A99B1) Tb2common::RemoveMessages
(004C6113) Tb2item::TTBView::EnterToolbarLoop
(004D3C32) Tb2toolbar::TTBToolbarView::EnterToolbarLoop
(0027DF90) Vcl::Controls::TControl::DoMouseDown
(0027DFDF) Vcl::Controls::TControl::WMLButtonDown
(00282491) Vcl::Controls::TWinControl::WndProc
(00281AD8) Vcl::Controls::TWinControl::MainWndProc
(003C9C14) System::Classes::_18201
(00040489) USER32.dll
(00037445) USER32.dll
(000351B5) USER32.dll
(00034F7B) 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.