Multiple Parent Pages

This is a problem within the Gutenberg editor. After creating a page, I want to place it under a parent page, so I go to the parent page dropdown (right). That dropdown is showing multiple instances of every page, structured under their parent pages, etc. It looks like the whole menu structure is just repeating 2 or 3 times. It also looks like some pages may be under one duplicated parent, but not another in the menu. I tried just resetting perma-links to see what happened but that didn’t have any effect.

Meanwhile, the website itself seems to be working properly. I can just work around it as long as the front end is correct, but it’s starting to get confusing.