<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 5.13.4

Error message:
External exception C0000006

Stack trace:
(0028B228) Vcl::Comctrls::TPageControl::WMEraseBkGnd
(0006248E) ntdll.dll
(0000F15E) ntdll.dll.KiUserExceptionDispatcher
(0025B9D5) Vcl::Controls::TWinControl::WndProc
(0025B01C) Vcl::Controls::TWinControl::MainWndProc
(00380D20) System::Classes::_18201
(000152F7) USER32.dll
(00015D35) USER32.dll
(0001FD3A) USER32.dll
(0001FD60) USER32.dll.CallWindowProcW
(00443C3B) Dragdrop::TDragDrop::WndMethod
(00380D20) System::Classes::_18201
(000152F7) USER32.dll
(00016311) USER32.dll.GetDC
(00015DE3) USER32.dll
(00015E41) USER32.dll
(0000F137) ntdll.dll.KiUserCallbackDispatcher
(0001F764) USER32.dll
(00019B23) atcuf32.dll
(00001D5A)atcuf32.dll

The problem happens rarely. I cannot reproduce it.