Why is there a category that I can't modify

[JammyDodger]

It could be the category name you picked. Someone had an issue with Finnish letters in this recent topic, and this was suggested as a solution:

Cannot delete or edit categories

If you can get to rails then you can do something like /var/discourse/launcher enter app rails c c=Category.find(123) c.name='safe name' c.save You’ll need to type a q to get out of the viewer after the find. 123 is the category I’d.