Ipad (9th gen) buttons not working

Ok so i was playing a racing game (real racing 3) on my iPad (9th gen), each time i try to brake it dosent work, then i tried to lower the volume but that didn't work, it was the same for the power and home button, the display was working but was not responding to my fingers however the lightning port and the headphone jack still worked and after i restarted the iPad the buttons started to work, do any of you know the cause of this problem?