The error message in your question appears to have been thrown from WP CLI. Based on your other comments the problem is that your theme is not properly declaring a global variable.
Somewhere in your code you have this declared outside a function:
$atp_theme = new ATP_theme();
Then in other parts of your code you have:
global $atp_theme;
When using WordPress via the browser, variables declared outside a function, like $atp_theme in that first line, are global. So you can access them by using global, like in the second line.
The problem is that when using WP CLI, variables declared outside a function are not automatically global. Therefore global $atp_theme is undefined.
To solve this you need to explicitly declare the variable as global when defining it, like this:
global $atp_theme;
$atp_theme = new ATP_theme();
Or this would also work:
$GLOBALS['atp_theme'] = new ATP_theme();