Helper Reproduction

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  type: 'all',
  init() {
    this.set('comment', this.comment1);
  },
  comment1: {
    parentComment: {
      isOpen: false,
    },
    isReply: true
  },
  comment2: {
    parentComment: {
      isOpen: true,
    },
    isReply: false
  },
});

helpers.comt-helper.js

import { helper as buildHelper } from '@ember/component/helper';

export default buildHelper(function(params) {
  let comment = params[0],
      type = params[1],
      retValue = false;
  
  switch (type) {
    case 'all':
      if(comment[0] !== undefined) {
        retValue = false;
      } else {
        retValue = true;
      }
      break;
    case 'unresolved':
      if(comment[0] !== undefined) {
        if((comment.filterBy('isOpen', true)).length > 0) {
          retValue = false;
        } retValue = true;
      } else if (comment.isReply && comment.parentComment.isOpen) {
        retValue = true;
      } else if (!(comment.isReply) && comment.isOpen) {
        retValue = true;
      }
      break;
    case 'resolved':
      if(comment[0] !== undefined) {
        if((comment.filterBy('isOpen', false)).length > 0) {
          retValue = false;
        }
        retValue = true;
      } else if (comment.isReply && comment.parentComment.isOpen !== true) {
        retValue = true;
      } else if (!(comment.isReply) && comment.isOpen !== true) {
        retValue = true;
      }
      break;
  }
  return retValue;
});

templates.application.hbs

<p>
{{#if (comt-helper comment type)}}
  All<br>
  comment.parentComment.isOpen: {{comment.parentComment.isOpen}}
{{else}}
  Unresolved<br>
  comment.parentComment.isOpen: {{comment.parentComment.isOpen}}
{{/if}}
</p>

<button {{action (mut type) 'unresolved'}}>Change to "Unresolved"</button>
<button {{action (mut type) 'all'}}>Change to "All"</button>
<br>
<button {{action (mut comment) comment1}}>Change to "comment1"</button>
<button {{action (mut comment) comment2}}>Change to "comment2"</button>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.0.0",
    "ember-template-compiler": "2.18.2",
    "ember-testing": "2.18.2"
  }
}