This is an issue that has been observed on Area 51 and now that phpBB.com is also running 3.2 it can be observed there as well. It appears that once a topic reply is disapproved or a user deleted, notifications that are associated to these post's topics are losing the title to the topic and show as empty quotes instead. The user "Anonymous" seems to also be showing for these notifications.
In the attachment both of these title-less notifications are for the "Discuss: phpBB 3.2 Rhea is upon us" topic. On A51 I see the same symptom but for several different topics.