One O365 Group > Two SharePoint Team Sites?

I know that when you create an O365 Group (through Outlook, or Teams, or Planner...maybe one other place), the provisioning engine creates a SharePoint site for that Group. However, I found a situation this morning where it seems we have two SharePoint sites that are linked to a single O365 Group.

The group is named "MaterialsOp" (as shown below, from our O365 Admin site):

However, in the SharePoint Admin Center, there are two sites with URLs starting with "MaterialsOp":

We have a script in place such that when folks create a group in Outlook, the user's UPN is attached to the end of the group name & URL as a means of quickly identifying the creator. So, the top site is the "original" site, created in October of 2017 when the group was created (the group has since been renamed to remove the "-by-<upn>"). The bottom one claims to have been created today at 7:31 AM (not sure if that's local/Eastern US time or UTC). They have the exact same members and when you go to either URL, the Conversations link takes you to the same mailbox. In fact, the "Activity" web part shows emails that have come into the mailbox and it's exactly the same on both sites. 

So, what could have caused a "new" site to be spawned today (at a time that neither myself nor any of the site/group members were accessing it)? It just doesn't make sense. 

If it matters (and it might), the original email address is still in place, but an alias has been added that replaces the "<tenantname>.onmicrosoft.com" with our local domain name.