Lockdown events had occurred due to too many failed login attempts or invalid us

Since upgrading to v5 and then v5.0.2 I’ve been getting email notifications with the subject “Site Lockdown Notification”

The email body starts:

[Lockdown events had occurred due to too many failed login attempts or invalid username:

Username: ]

The username is blank, there is an IP shown. I check WP Security > User Login > Failed Login Records; however, nothing is displayed in the list.

Is this an actual user or someone trying to login without credentials and picked up by your plugin. I think since the upgrade I added my email address to be notified out of curiosity, so maybe this was happening previously and I’ve only just now been getting notifications.

Iain