Furnaces do not smelt armor pieces anymore

As you can see in the attached images, furnaces in my world stopped being able to smelt armor pieces. However, they still are able to smelt certain tools like iron shovels. 

 

World Folder Link (Google Drive):

https://drive.google.com/drive/folders/1HQyce-GJ3MS-TO8TZ_VOD9ubiFngzb_M?usp=sharing