[Django]-Wagtail 4.1, 'NoneType' object has no attribute '_inc_path'

'NoneType' object has no attribute '_inc_path' usually indicates that the internal fields (path, depth, numchild) defined by the django-treebeard library for keeping track of child counts in the page tree have become inconsistent. It’s unclear what might have caused that here, but running ./manage.py fixtree should fix it.