We solved an issue introduced by a change in Microsoft 365 that could cause members of a Microsoft 365 group to become site collection admins in a site collection associated with a team created in Provisioning with a blueprint site.
This incident could occur when a source site was used as a blueprint site for your template.
When you create teams via templates with an active blueprint, a new site collection is generated and merged with the blueprint site.
During that process, members of the source site could end up as site collection admins in the new site collection.
We have not yet determined when Microsoft implemented that change and the scope of this problem. We'll continue investigating this issue and reaching out to affected customers as more information becomes available.
If you have recently used blueprint sites to create new teams, we suggest that you verify your site collection admins at the destination.