It’s not getting destroyed (you can still see it in the hierarchy). The reference is getting set to null because in CheckIfBallColorIsDifferent line 21, you set it to GetComponent(). There isn’t a CountDown on the object on which that script is running, so that becomes null.
I’d like to add that I find your code very confusing. Some of your names make no sense at all. For example “currentTime” implies it’s some time value, thus a number, but it’s a bool. Then you have “showCountDown” which one would assume to be a boolean, but it’s a GameObject. Things like these make it increadibly hard to follow your code.
I’d also prefer the code to be posted using code tags, since switching tabs is kinda inconvenient.
Even if paste of code looks nice.