Some users reported that if they have the subscribe module activated and an email is added in the subscribe field, it doesn't appear in Modules -> Subscribe -> Stats, that number remains 0. I tried to replicate this on multiple instances, but for me it works properly every time. However, there are a couple of users that encounter this issue, so maybe there is something happening here. One of them said that after he adds an email, a security popup like the one from this issue appears for him, but it doesn't appear for me.

Reported here and here.