@hernandezmachava take a look at the option set with the following API call:
[your instance URL]/api/optionSets/nC3j3WeXKbU?fields=*,options[name,id,sortOrder]
All the options should have a code and the sort order should be sequential starting from 1, if that is not the case then you’ll have to replace any options missing the code and try to sort by name or code, then test again.