It seems youtube changed their embedded code, and this breaks demoiframe. But the good news is that there is a better way to click inside iframes: Use XClick (image).
Example screencast (just two commands needed!):
Macro (add your own image):
{
"Name": "youtube",
"CreationDate": "2018-12-20",
"Commands": [
{
"Command": "open",
"Target": "https://a9t9.com/kantu/demo/iframes",
"Value": ""
},
{
"Command": "click",
"Target": "//*[@id=\"content\"]/div[2]/div/p[5]",
"Value": ""
},
{
"Command": "XClick",
"Target": "button-image-here.png",
"Value": ""
}
]
}