<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 5.15.9

Error message:
Failed to set tab "" at index 1

Traza de la pila:
(002A5335) Vcl::Comctrls::_16736
(002A782A) Vcl::Comctrls::TPageControl::UpdateTab
(002A6B53) Vcl::Comctrls::TTabSheet::SetImageIndex
(0001FED8) TCustomScpExplorerForm::DoTerminalListChanged
(0001FF88) TCustomScpExplorerForm::TerminalListChanged
(0000689D) TCustomScpExplorerForm::WMCopyData
(00027301) TCustomScpExplorerForm::Dispatch
(00279219) Vcl::Controls::TWinControl::WndProc
(002336E0) Vcl::Forms::TCustomForm::WndProc

The problem happens rarely. I cannot reproduce it.