xflock4 does not lock the screen if the screensaver is disabled in settings

This is clearly wrong, since the very point of disabling a screensaver in the Settings is to lock the screen manually when needed.

Locking the screen with xscreensaver also fails, since "xfce4-screensaver is already running".

I suggest making sure that xfce4-screensaver is never running if the screensaver is disabled in the settings (perhaps by periodically polling the process space).