When the RCSSFBSVR server get rebooted the ‘Skype for Business Server Front-End Service’ will not start always and when you tried to start this service manually the operation will fail. This server need a subsequent reboot to fix this issue. After doing the second reboot please verify that the ‘Skype for Business response group’ service is started. I have seen sometimes this service starts and then stops before the ‘Skype for Business Server Front-End Service’ starts. In that case you will need to manually start this service after the ‘Skype for Business Server Front-End Service’ started.