When editing a Sub-process blueprint. You should have edited the Sub-process blueprint in "Global templates and blueprints" section in the administration area. Whenever you edit one of the blueprints, the Confluence is creating automatically a so-called index page when you try to create a page from that blueprint. The index page is created only once and does not have any impact on the usability of the app.
This is an Atlassian behavior that affects Process Management Suite for Confluence app as well. Unfortunately, there is no workaround for this issue and technically can not be solved in our side.