<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 5.9.4

Error message:
Invalid access to memory.

Stack trace:
(001B2960) Vcl::Stdctrls::TCustomEdit::GetModified
(0003EE3E) ntdll.dll.ZwWow64CallFunction64
(0003F5BA) ntdll.dll.KiUserExceptionDispatcher
(00061F0A) TEditorManager::ProcessFiles
(00010FDF) TCustomScpExplorerForm::AnyInternalEditorModified
(003B5400) System::Actions::TContainedActionList::UpdateAction
(0019C52E) Vcl::Actnlist::TCustomAction::Update
(0020E396) Vcl::Forms::_16777
(0020E414) Vcl::Forms::TCustomForm::UpdateActions

The problem happens rarely. I cannot reproduce it.