Debug Settings are an advanced tool that can help resolve issues with your account. Be careful when accessing them, as some changes can have unintended effects!
Enabling Debug Settings
To enable the Debug Settings Menu, click on the NovelAI logo in the top left 20 times. After that you can open the Settings and access the Debug Settings.
Deleting Inaccessible Stories
Enable the Debug Settings and select the "Debug Story Deletion" option.
Find the ID in the address bar when the affected story is selected, Example;
Enter the ID in the Debug Field and click Delete. The story should now be gone after you refresh.