If you were there for 4 months, were you able to show in your NOA that you had a job and had earned enough in the year prior to you having applied? I guess that is where they are having an issue - firstly, since you haven't spent enough time - they want to know whether you yourself have enough financial standing to afford a second person. Secondly - Canadian government loves taxes and it seems you wouldn't have paid nearly enough in 4 months. So 'eligibility' will probably be taking longer.
Again - like most - this is just a guess, but it seems to be a common theme for applicants who have recently arrived and applied to sponsor wife to go through longer scrutiny.