Even with the perfect setup, ultralight work presents unique glitches. Here is how to solve them:
: In the UMP interface, navigate to the Resourcepacks dialog to select and activate your desired pack.
Open the resource pack .zip file. Ensure the folder structure begins immediately with assets rather than a wrapper folder. Inside assets/minecraft/ , look for the sounds.json file. Ensure this file hasn't been corrupted or overwritten by another texture pack higher up in your load order.