Why showing bugs in sample code of space shooting project

Hello I am new here, recently I downloaded space shooter sample project , ran and compiled it .. everything was running fine but since last two days it is showing problems in bullet when i move my spaceship player don't shoot , Also sometimes it doesn't shoot at all ..and asteroids which are exiting boundary also not getting deleted automatically.. in starting everything was running fine .don't know how it is happening...I tried on both Unity 5.5.4 and Unity 5.6.1 ...but showing problem in both versions