"should" and "is" are... arguing. :) This is my first time, and I do see the server (I installed my own) "see" the message counter increase! The logs show an increase of +1 with your new reply (and it shows all 3 now as log lines). So my push server is getting an event.
Yet on my mobile (which is showing connected and monitoring the "topic") is not popping up an event notification. I've just enabled the "Record Logs" feature in the ntfy android app as a next debug step. Adventure!