There could be a lot of reasons for GU.Hi Everyone:
I received AOR on 13th June, 2019 and passed the medical on July 18th, 2019. I applied from the US and then moved to India in October. I notified CIC that I have moved to India in October itself. After 2-3 months of waiting, I got an email on 27th Jan, 2020 from CIC asking me to confirm my address in India. On the very same day, the profile changed to "Application/profile updated" for a few hours and then changed to "Submitted" again. I suppose that this is the ghost update. Do you know how long can it take to receive the passport request after the ghost update.
To name a few, when they initiate your security check, when your eligibility passes, when they finalize your security check, etc.
So GU could mean a lot of things.