This bug has been added to the tracker:
https://winscp.net/tracker/1817

<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)>

!!You alrady got a Debug logfile!!

WinSCP 5.16.5

Error message:
Invalid access to memory.

Stack trace:
(00009294) TCustomScpExplorerForm::SetTaskbarListProgressState
(0112D2F6) C5310_3
(0112F35E) ____ExceptionHandler
(0112C118) __ExceptionHandler
(00087D6F) ntdll.dll
(00073211) ntdll.dll.KiUserExceptionDispatcher
(000092E0) TCustomScpExplorerForm::SetTaskbarListProgressValue
(000273B7) TCustomScpExplorerForm::TerminalSynchronizeDirectory
(00F2C118) TTerminal::DoSynchronizeProgress
(00F278E1) TTerminal::DoSynchronizeCollectDirectory
(00F2661F) TTerminal::SynchronizeCollect
(00026C08) TCustomScpExplorerForm::DoFullSynchronizeDirectories
(00066C02) TScpCommanderForm::FullSynchronizeDirectories
(0005C109) TNonVisualDataModule::ExplorerActionsExecute
(004E695C) System::Actions::TContainedActionList::ExecuteAction
(002DDBEA) Vcl::Actnlist::TCustomAction::Execute
(004B1223) System::Classes::TBasicActionLink::Execute
(005BDE32) Tb2item::TTBCustomItem::ClickWndProc
(004B2094) System::Classes::_18201
(000436C9) USER32.dll
(000250B7) USER32.dll
(00024209) USER32.dll
(00023FCB) USER32.dll.DispatchMessageW
(00258E5F) Vcl::Forms::TApplication::ProcessMessage
(00258EAF) Vcl::Forms::TApplication::HandleMessage
(00259263) Vcl::Forms::TApplication::Run
(0012983C) Execute
(0000315D) wWinMain
(0112B309) __wstartup
(00066B72) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00066B3F) ntdll.dll.RtlGetAppContainerNamedObjectPath

(0112D961) C5310_3
(0112EF3B) _ReThrowException
(00F266AC) TTerminal::SynchronizeCollect
(00026C08) TCustomScpExplorerForm::DoFullSynchronizeDirectories
(00066C02) TScpCommanderForm::FullSynchronizeDirectories
(0005C109) TNonVisualDataModule::ExplorerActionsExecute
(004E695C) System::Actions::TContainedActionList::ExecuteAction
(002DDBEA) Vcl::Actnlist::TCustomAction::Execute
(004B1223) System::Classes::TBasicActionLink::Execute
(005BDE32) Tb2item::TTBCustomItem::ClickWndProc
(004B2094) System::Classes::_18201
(000436C9) USER32.dll
(000250B7) USER32.dll
(00024209) USER32.dll
(00023FCB) USER32.dll.DispatchMessageW
(00258E5F) Vcl::Forms::TApplication::ProcessMessage
(00258EAF) Vcl::Forms::TApplication::HandleMessage
(00259263) Vcl::Forms::TApplication::Run
(0012983C) Execute
(0000315D) wWinMain
(0112B309) __wstartup
(00066B72) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00066B3F) ntdll.dll.RtlGetAppContainerNamedObjectPath

(00009294) TCustomScpExplorerForm::SetTaskbarListProgressState
(00087D6F) ntdll.dll
(00073211) ntdll.dll.KiUserExceptionDispatcher
(00026D20) TCustomScpExplorerForm::DoFullSynchronizeDirectories
(00066C02) TScpCommanderForm::FullSynchronizeDirectories
(0005C109) TNonVisualDataModule::ExplorerActionsExecute
(004E695C) System::Actions::TContainedActionList::ExecuteAction
(002DDBEA) Vcl::Actnlist::TCustomAction::Execute
(004B1223) System::Classes::TBasicActionLink::Execute
(005BDE32) Tb2item::TTBCustomItem::ClickWndProc
(004B2094) System::Classes::_18201
(000436C9) USER32.dll
(000250B7) USER32.dll
(00024209) USER32.dll
(00023FCB) USER32.dll.DispatchMessageW
(00258E5F) Vcl::Forms::TApplication::ProcessMessage
(00258EAF) Vcl::Forms::TApplication::HandleMessage
(00259263) Vcl::Forms::TApplication::Run
(0012983C) Execute
(0000315D) wWinMain
(0112B309) __wstartup
(00066B72) ntdll.dll.RtlGetAppContainerNamedObjectPath
(00066B3F) ntdll.dll.RtlGetAppContainerNamedObjectPath

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.

<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 5.16.4

Error message:
Zugriffsverletzung - ungültiger Zugriff auf den Speicher.

Stack trace:
(000079B5) TCustomScpExplorerForm::SetTaskbarListProgressState
(00F85386) C5296_0
(00F873EE) ____ExceptionHandler
(00F841A8) __ExceptionHandler
(00087D6F) ntdll.dll
(00073211) ntdll.dll.KiUserExceptionDispatcher
(00DA1C2F) TTerminal::DoSynchronizeProgress
(00D9BD26) TTerminal::SynchronizeCollect
(0001DFB0) TCustomScpExplorerForm::DoFullSynchronizeDirectories
(0004FD36) TScpCommanderForm::FullSynchronizeDirectories
(00047BD8) TNonVisualDataModule::ExplorerActionsExecute
(003E7BFC) System::Actions::TContainedActionList::ExecuteAction
(001C67E5) Vcl::Actnlist::TCustomAction::Execute
(003A41D8) System::Classes::_18201
(000436C9) USER32.dll
(000250B7) USER32.dll
(00024209) USER32.dll
(00023FCB) USER32.dll.DispatchMessageW

(00F859F1) C5296_0
(00F86FCB) _ReThrowException
(00D9BD71) TTerminal::SynchronizeCollect
(0001DFB0) TCustomScpExplorerForm::DoFullSynchronizeDirectories
(0004FD36) TScpCommanderForm::FullSynchronizeDirectories
(00047BD8) TNonVisualDataModule::ExplorerActionsExecute
(003E7BFC) System::Actions::TContainedActionList::ExecuteAction
(001C67E5) Vcl::Actnlist::TCustomAction::Execute
(003A41D8) System::Classes::_18201
(000436C9) USER32.dll
(000250B7) USER32.dll
(00024209) USER32.dll
(00023FCB) USER32.dll.DispatchMessageW

(000079B5) TCustomScpExplorerForm::SetTaskbarListProgressState
(00087D6F) ntdll.dll
(00073211) ntdll.dll.KiUserExceptionDispatcher
(0004FD36) TScpCommanderForm::FullSynchronizeDirectories
(00047BD8) TNonVisualDataModule::ExplorerActionsExecute
(003E7BFC) System::Actions::TContainedActionList::ExecuteAction
(001C67E5) Vcl::Actnlist::TCustomAction::Execute
(003A41D8) System::Classes::_18201
(000436C9) USER32.dll
(000250B7) USER32.dll
(00024209) USER32.dll
(00023FCB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.

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.

<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 5.16.2

Error message:
Invalid access to memory.

Stack trace:
(000079B5) TCustomScpExplorerForm::SetTaskbarListProgressState
(00F830CE) C5296_3
(00F85136) ____ExceptionHandler
(00F81EF0) __ExceptionHandler
(0008402F) ntdll.dll
(00071931) ntdll.dll.KiUserExceptionDispatcher
(00DA13C7) TTerminal::DoSynchronizeProgress
(00D9B4BE) TTerminal::SynchronizeCollect
(0001B27C) TCustomScpExplorerForm::Synchronize
(0001AD05) TCustomScpExplorerForm::DoSynchronize
(000A94A2) TSynchronizeController::StartStop
(00E3050E) TSynchronizeDialog::DoStartStop
(00E30C43) TSynchronizeDialog::Start
(00E30A86) TSynchronizeDialog::StartButtonClick
(002794B1) Vcl::Controls::TWinControl::WndProc
(001E1640) Vcl::Stdctrls::TButtonControl::WndProc
(00279617) Vcl::Controls::_17076
(002794B1) Vcl::Controls::TWinControl::WndProc
(00233978) Vcl::Forms::TCustomForm::WndProc

(00F83739) C5296_3
(00F84D13) _ReThrowException
(00D9B509) TTerminal::SynchronizeCollect
(0001B27C) TCustomScpExplorerForm::Synchronize
(0001AD05) TCustomScpExplorerForm::DoSynchronize
(000A94A2) TSynchronizeController::StartStop
(00E3050E) TSynchronizeDialog::DoStartStop
(00E30C43) TSynchronizeDialog::Start
(00E30A86) TSynchronizeDialog::StartButtonClick
(002794B1) Vcl::Controls::TWinControl::WndProc
(001E1640) Vcl::Stdctrls::TButtonControl::WndProc
(00279617) Vcl::Controls::_17076
(002794B1) Vcl::Controls::TWinControl::WndProc
(00233978) Vcl::Forms::TCustomForm::WndProc

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.

OK with previous version, the new one bugs when comparing subfolders.