Had a strange issue that happened when I was quickly undoing multiple times, and then redoing all the undos, then saved.
It caused many elements to be duplicated. By the looks of it, every element after Section > Container gets duplicated. The duplicated elements has the same ID as well, so there’s no way to delete the duplicates as deleting one of them will delete all with the same IDs. The only work around I have was to revert to a slightly earlier revision that doesn’t have this problem.