Stefan Krusche wrote:
>> Am Sonntag 18 Dezember 2016 schrieb Michele Calgaro:
>> Kate -> Settings -> Configure Kate -> Session: provides option for
>> session management when opening and closing Kate. In particular if
>> you choose "Manually choose session" you will be presented with a
>> dialog where to select the session to use when you start Kate

> After you close kate and start it again with no arguments a dialog
> will pop up and ask for which session to open. In that dialog you
> can choose your preferred session and click the button for keeping
> it permanently as your default session.

That is the long route to setting 'last-used session'. As I said:

"Settings > configure > sessions > save session (last-used saves open
docs, new session doesn't)."

Select the Settings 'save session' option to save the current session
configuration, e.g. the OP's hidden sidebars and documents tool views.

Select 'start new session' to get a blank slate every time Kate starts.
Select 'load last used session' to reopen any files left open in the
previous session.

What you did was set 'load last used session' via the 'choose session'
menu checkbox. The only reason to select 'choose session' is if you
want to choose a saved session during Kate startup.