<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 5.9.6

Error message:
Invalid access to memory.

Stack trace:
(0064BA05) TFileOperationProgressType::TotalTimeLeft
(008689AA) D1576_1
(0086AA12) D1576_1
(008677CC) D1576_1
(000888DF) ntdll.dll
(0006FEE1) ntdll.dll.KiUserExceptionDispatcher
(00648D12) TFileOperationProgressType::Start
(00649217) TFileOperationProgressType::SetSpeedCounters
(0064D29D) TFTPFileSystem::Open
(0064D39D) TFTPFileSystem::Open
(00618CF9) TCustomUnixDriveView::NodePathName
(0061EEC7) CutToChar
(0062B869) Configuration::C2308_0
(006FAA1B) TSFTPFileSystem::SFTPSource
(00771C0A) TPreferencesDialog::SaveConfiguration
(006C739C) TStoredSessionList::ImportHostKeys
(006C5878) TStoredSessionList::DoSave
(00098E9B) TWinConfiguration::GetUpdates
(00017642) KERNEL32.DLL.BaseThreadInitThunk
(00063FB5) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00063F82) ntdll.dll.RtlGetAppContainerNamedObjectPath

(00869015) D1576_1
(0086A5EF) D1576_1
(006FABD8) TSFTPFileSystem::SFTPSource
(00771C0A) TPreferencesDialog::SaveConfiguration
(006C739C) TStoredSessionList::ImportHostKeys
(006C5878) TStoredSessionList::DoSave
(00098E9B) TWinConfiguration::GetUpdates
(00017642) KERNEL32.DLL.BaseThreadInitThunk
(00063FB5) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00063F82) ntdll.dll.RtlGetAppContainerNamedObjectPath

(00869015) D1576_1
(0086A5EF) D1576_1
(00771D9F) TPreferencesDialog::SaveConfiguration
(006C739C) TStoredSessionList::ImportHostKeys
(006C5878) TStoredSessionList::DoSave
(00098E9B) TWinConfiguration::GetUpdates
(00017642) KERNEL32.DLL.BaseThreadInitThunk
(00063FB5) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00063F82) ntdll.dll.RtlGetAppContainerNamedObjectPath

(00869015) D1576_1
(0086A5EF) D1576_1
(007722FD) TPreferencesDialog::SaveConfiguration
(006C739C) TStoredSessionList::ImportHostKeys
(006C5878) TStoredSessionList::DoSave
(00098E9B) TWinConfiguration::GetUpdates
(00017642) KERNEL32.DLL.BaseThreadInitThunk
(00063FB5) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00063F82) ntdll.dll.RtlGetAppContainerNamedObjectPath :P

The problem happens rarely. I cannot reproduce it.