Lead Developer
Sections are saved as a serialized table in the database. When people do a search/replace for their URL in the database, it breaks serialized tables (not just Sections, but any serialized tables).
That’s why plugins like BackupBuddy, Duplicator, Updraft Plus etc.. are so useful, as they take care of issues like this for you.
Those warnings are happening because the page thinks it should have sections, but those sections no longer exist in the database, most likely due to search and replacing of URLs.
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development