Ember: Uncaught TypeError: t.addArrayObserver is not a function

So this is a more general question as my code base is huge and still not able to figure out which part is throwing the issue. But I keep encountering this quite often. Only thing I think I know is it's coming from some observer on an array.

Can someone please just explain the error like why it might be thrown or what are the good practice for observers so that I can find that issue and try not to cause it in future.

Note: There is no issue in development environment, causes an issue once in production environment.