WDIO test runner unable to find cucumber step definitions

When executing the WDIO test runner with

$ ./node_modules/.bin/wdio wdio.conf.js

a new Chrome window (as I have configured) pops up briefly and I get:

ERROR: ENOENT: no such file or directory, lstat '/Users/me/path/to/app/features/step_definitions/**'

Meanwhile, I have:

1. Installed the Cucumber framework: wdio-cucumber-framework
2. Set wdio.conf.js file to framework: 'cucumber'
3. Am using the default wdio generated cucumberOpts, except for require where I used step_definitions instead of step-definitions:

    cucumberOpts: {
        require: ['./features/step_definitions/**/*.js'],        // <string[]> (file/dir) require files before executing features
        backtrace: false,   // <boolean> show full backtrace for errors
        compiler: [],       // <string[]> ("extension:module") require files with the given EXTENSION after requiring MODULE (repeatable)
        dryRun: false,      // <boolean> invoke formatters without executing steps
        failFast: false,    // <boolean> abort the run on first failure
        format: ['pretty'], // <string[]> (type[:path]) specify the output format, optionally supply PATH to redirect formatter output (repeatable)
        colors: true,       // <boolean> disable colors in formatter output
        snippets: true,     // <boolean> hide step definition snippets for pending steps
        source: true,       // <boolean> hide source uris
        profile: [],        // <string[]> (name) specify the profile to use
        strict: false,      // <boolean> fail if there are any undefined or pending steps
        tags: [],           // <string[]> (expression) only execute the features or scenarios with tags matching the expression
        timeout: 20000,     // <number> timeout for step definitions
        ignoreUndefinedDefinitions: false, // <boolean> Enable this config to treat undefined definitions as warnings.
    },

If I were to run $ cucumber.js from the command line it would read my file: features/step_definitions/auth/login.js

Yet, the WDIO test runner doesn’t appear to be able to do this, and from the error message, it appears the search path is truncated since I don’t see a /*.js

What can I do here to get cucumber to read my step definitions using the WDIO test runner? Thanks.