"MODULE_DOES_NOT_EXIST" when trying to utilize @NAmdConfig

@NApiVersion

My modules file is located at "SuiteScripts/Config/modules.json" and contains the following contents:

{

    "paths": {

        "prefUtils": "SuiteScripts/Modules/Pref.js"

    }

}

In a Suitelet file, the following is at the top:

/**

* @NApiVersion 2.1

* @NScriptType Suitelet

* @NAmdConfig /SuiteScripts/Config/modules.json

*/

define('prefUtils'], function (prefUtils) {

.....

However this script errors with the message:

{"type":"error.SuiteScriptModuleLoaderError","name":"MODULE_DOES_NOT_EXIST","message":"Module does not exist: /prefUtils.js","stack":[]}

It's as if the module config file isn't getting recognized.

Replacing

define('prefUtils'], function (prefUtils) {

with

define('SuiteScripts/Modules/Pref.js'], function (prefUtils) {

does not cause any error.

I swear it worked fine a week or two ago when I first discovered this, but nothing I've tried will work now.