Default member group permissions editable

We all know that default sharepoint groups (Owners, Members, Visitors) are created automatically and their permissions can’t be changed. It is recommended to copy/create new groups and assign the user <sharepoint name> Members to it if we need to adjust permissions for members.

Today, in the permissions page, I selected the Members group and the permissions were suddenly editable. Why and how this happened? Is it something that needs to be fixed/could cause problems later? Owners and Visitors are still un-editable.

This is a new model sharepoint online site.

Thanks,