Monaco deltaDecorations not working with angular 7

I m trying to use Monaco Editor in an app I am currently developing and I need to highlight some lines of the code displayed in the editor. I m currently using the angular component ngx-monaco-editor (www.npmjs.com/package/ngx-monaco-editor) for this.

I saw in the Monaco playground a way to do what I want using the following: (https://microsoft.github.io/monaco-editor/playground.html#interacting-with-the-editor-rendering-glyphs-in-the-margin)

var decorations = editor.deltaDecorations([], [
    {
        range: new monaco.Range(3,1,3,1),
        options: {
            isWholeLine: true,
            className: 'myContentClass',
            glyphMarginClassName: 'myGlyphMarginClass'
        }
    }
]);

Using the angular component, I can have access to the editor object using the onInit event emitter. I also compared the object from the component and in the playground and they have the same properties so I assumed they were the same. To test it outside of the big app, I started a little angular project following the ngx-monaco-editor documentation to have matching code to compare. However, in the playground the line is correctly highlighted while it is not in my app.

I looked at the issues on the angular component and saw nothing of the sort. Moreover, it says that it supports every features provided by monaco. I checked that I use the same version for angular and monaco and they are the same.

I tried to reproduce the playground example using the angular component:

app.component.html

<ngx-monaco-editor [options]="editorOptions" [(ngModel)]="code" (onInit)="onInit($event)"></ngx-monaco-editor>

app.component.ts

editorOptions = {
    theme: 'vs',
    language: 'javascript',
    glyphMargin: true
  };
code = [
    '"use strict";',
    'function Person(age) {',
    '   if (age) {',
    '       this.age = age;',
    '   }',
    '}',
    'Person.prototype.getAge = function () {',
    '   return this.age;',
    '};'
  ].join('\n');

onInit(editor: any) {
  const t = editor.deltaDecorations([], [
    {
      range: new monaco.Range(3, 1, 3, 1),
      options: {
        isWholeLine: true,
        className: 'myContentClass',
        glyphMarginClassName: 'myGlyphMarginClass'
      }
    }
  ]);
  console.log(t);
}

app.component.css

.myGlyphMarginClass {
    background: red;
}
.myContentClass {
    background: lightblue;
}

I checked with logs that the decorations are correctly initilized and created, but they are the same from the playground and the console.