I saw it on this site and on other sites I manage, but never on my Axivo site. Yesterday I did a test and subscribed to a thread while having a friend posting replies and clicking on Likes. I was browsing the forums into different locations, while he was performing the related actions I just mentioned. I never got the popup, but did saw the red balloon displaying the new alerts. I don't have any template edits, stock Xenforo software.
Thank you for your help.