For the last two levels I reached (23 and 24) I didn't get the notification, pop-up or wall post that I normally get.
I level up by replying to topics and owls as well as doing and grading homework. I also ate and drunk recently because my schedule didn't allow me to visit the Great Hall on time for the meals, so maybe I did reach level 24 after purchasing or eating something. I am not sure.
I reached level 23 three or four days ago and level 24 today (2 April).
I have checked other people's profiles that reached the same levels recently and they have the wall posts for those levels.
I hope this information helps. I will be happy to answer any question that may help fix this issue.
Thank you in advance!
Customer support service by UserEcho