Wordfence: Notice in Live Activity report

I just got this message at the top of the Live Traffic page this morning:

Notice: Undefined index: coreUnknown in /home/uniqueb/public_html/wp-content/plugins/wordfence/lib/wordfenceHash.php on line 141

I’m using the latest version (free) of Wordfence Security: 6.1.12.

Does anyone know anything about this? Is this a problem or just a minor thing?