Is the Broadcast feature Not Working or Stopped Working? Of course there are varied reasons that comes in play, starting with report/column access to user, data source access to user, connectivity to the AR Server/Datasource, SMTP Server File Size limitations etc. Only if we have the error then we can determine the area to focus & so the fix.
Nevertheless, below in the link that lets you enable the Broadcast DEBUG logs to capture more on what is happening in the background:
If it was working earlier then stopped working and considering hprof files are being generated may be a simple restart can fix the issue too.
Note: If feasible change the Initial Memory Pool value to match it with Max Memory Pool. I see no harm in doing it unless there are other applications hosted on same box that await for the memory to be released time to time.
Hope this helps.