Problem with many selectors - test images are blank or not exactly on selector

Hi everyone,

We have a problem rendering test images with backstop and puppeteer.
We have many selectors to test and everytime we run _backstop test_ rendered images are blank, not well positioned and some are good...

Here is a screenshot of the result

Heres the backstop.json:

{

  "id": "backstop_default",

  "viewports": [

    {

      "label": "phone",

      "width": 320,

      "height": 480

    },    

    {

      "label": "tablet",

      "width": 1024,

      "height": 768

    }

  ],

  "onBeforeScript": "puppet/onBefore.js",

  "onReadyScript": "puppet/onReady.js",

  "scenarios": [

    {

      "label": "BackstopJS Homepage",

      "cookiePath": "backstop_data/engine_scripts/cookies.json",

      "url": "https://icomoon.io/#preview-free",

      "referenceUrl": "",

      "readyEvent": "",

      "readySelector": "#glyphs3",

      "delay": 10000,

      "hideSelectors": [],

      "removeSelectors": [],

      "hoverSelector": "",

      "clickSelector": "",

      "postInteractionWait": 0,

      "scrollToSelector": "div.unit.glyph",

      "selectors": ["div.unit.glyph"],

      "selectorExpansion": true,

      "misMatchThreshold": 0.1,

      "requireSameDimensions": true

    }

  ],

  "paths": {

    "bitmaps_reference": "backstop_data/bitmaps_reference",

    "bitmaps_test": "backstop_data/bitmaps_test",

    "engine_scripts": "backstop_data/engine_scripts",

    "html_report": "backstop_data/html_report",

    "ci_report": "backstop_data/ci_report"

  },

  "report": ["browser"],

  "engine": "puppeteer",

  "engineOptions": {

    "args": ["--no-sandbox"]

  },

  "asyncCaptureLimit": 1,

  "asyncCompareLimit": 1,

  "debug": false

}

BTW, the url in this exemple reproduce the same problem we have on our app ( private ).

Thank you for your help all!