Found the solution: Due to a hang I pressed the reset button. This caused the BIOS think something with overclocking went wrong and set everything back to default. This also has set the SATA interfaces back to IDE emulation. Switching back to AHCI brought back the IAStoreDataSvc to normal and the UI also works. I could reinstall RST now. Between this BIOS reset and me detecting the problem a few days passed so I didn't made that connection.
It would've been nice if the setup or the app would've told me, that there was no AHCI enabled port!