Backstopjs site loading issue not solved by delay: what is wrong? - json

Question

When I try to run backstopjs on certain sites (they all must have some dynamic rendering thing in common, though I don't know what), the screenshots generated by backstopjs only include the first piece of content, centered in the screen. Here's the URL to a screenshot: https://user-images.githubusercontent.com/41495147/63806833-1612b680-c8e2-11e9-9932-680864b470b7.png
I've already tried setting the delay to 5 seconds. I've tried waiting until the footer class is available before screenshot. No dice. What is going on? Here's my config file:
"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
}```