Recently I had joined to Space Exploration community. Though I have receive 100 association bonus point, wrong number was shown as notification.
It looks like you had lost 33 reputation prior to gaining this association bonus. See Why do reputation drops not highlight the Achievements icon?
The reason the loss of that 33 reputation is not shown in the dialog is because it's lost via a post deletion, and deleted posts don't show up in the achievements dialog.
It's not a bug indeed. I am expecting status-bydesign.