Error reading CustomScpExplorerForm.OnClose: Invalid property value - System::Classes::TReader::ReadPropValue

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
Tried opening WinSCP after coming home from work to continue development on my website. No longer wants to open, yields the error + stack trace as given below.
Neither of the report options are valid;
- the issue is persistent
- I do not know how to produce this error from scratch. It just happened, and it doesn't go away.

<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 5.9.6

Error message:
Error reading CustomScpExplorerForm.OnClose: Invalid property value

Stack trace:
(003624DD) System::Classes::_17617
(00364AB4) System::Classes::TReader::ReadPropValue
(0036457A) System::Classes::TReader::ReadProperty
(00363DCD) System::Classes::TReader::ReadDataInner
(00363D80) System::Classes::TReader::ReadData
(00371971) System::Classes::TComponent::ReadState
(00208A2D) Vcl::Forms::TCustomForm::ReadState
(00364D5B) System::Classes::TReader::ReadRootComponent
(0035EC26) System::Classes::TStream::ReadComponent
(0035466B) System::Classes::_17089
(00355FBF) System::Classes::_17116
(00355F94) System::Classes::_17116
(0035604D) System::Classes::InitInheritedComponent
(00208226) Vcl::Forms::TCustomForm::TCustomForm
(00003FC6) Vcl::Forms::TForm::TForm
(000036D9) TCustomScpExplorerForm::TCustomScpExplorerForm
(0003FC82) TScpCommanderForm::TScpCommanderForm
(002131D6) Vcl::Forms::TApplication::CreateForm
(00811137) _SafeFormCreate
(000024A8) wWinMain
(008669E1) __wstartup
(0005FFD7) ntdll.dll
(0005FF9F) ntdll.dll

(0036439F) System::Classes::_17687
(003645D9) System::Classes::TReader::ReadProperty
(00363DCD) System::Classes::TReader::ReadDataInner
(00363D80) System::Classes::TReader::ReadData
(00371971) System::Classes::TComponent::ReadState
(00208A2D) Vcl::Forms::TCustomForm::ReadState
(00364D5B) System::Classes::TReader::ReadRootComponent
(0035EC26) System

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.

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.