I have noticed a red numerical notifacation badge in AdminCP under System > Applications

I don't see anything in the list of applications that needs attention.

What does this mean, and how do I resolve it. It's got my OCD going crazy! 😬

Unfortunately, this is not something which I can see on your community's ACP. Was it resolved? However, it usually will indicate an application which needs upgrading. 

You were right it was an update for an addon.

I think the update available bubble should be red to help locate the issue.