Delay doesn't fix screenshot

Why, when I try to take screenshots of certain sites, do they end up looking like this:
Here's my config (in which I set the delay to 5 freaking seconds and tried to make it wait until the footer had loaded before I took the screenshot):
`{
"id": "backstop_default",
"viewports": [
{
"label": "phone",
"width": 320,
"height": 480
},
{
"label": "tablet",
"width": 1024,
"height": 768
},
{
"label": "desktop",
"width": 1280,
"height": 1024
}
],
"onBeforeScript": "puppet/onBefore.js",
"onReadyScript": "puppet/onReady.js",
"scenarios": [
{
"label": "VMLYR Home",
"cookiePath": "backstop_data/engine_scripts/cookies.json",
"url": "https://www.vmlyr.com",
"referenceUrl": "",
"readyEvent": "",
"readySelector": ".region-footer",
"delay": 5000,
"hideSelectors": [],
"removeSelectors": [],
"hoverSelector": "",
"clickSelector": "",
"postInteractionWait": 0,
"selectors": [],
"selectorExpansion": true,
"expect": 0,
"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": 5,
"asyncCompareLimit": 50,
"debug": false,
"debugWindow": false
}`

Start by reproducing the scenario with the supplied BackstopJS configuration and inspect how the Puppeteer engine handles readySelector and delay, including puppet/onReady.js. Compare the capture timing with the footer-loading behavior at the supplied URL. Done means the configured wait reliably produces a complete screenshot, with a regression test or documented reproduction.

Written by the indexing model from the issue text.