Google platform.js有时不触发onload回调

如果我按特定顺序加载其他javascript源,下面的代码将不会调用platform_callback。

<script type="text/javascript" src="//apis.google.com/js/platform.js?onload=platform_callback" async defer></script> 
<script>
    function platform_callback() {
        console.log("callback");
    }
</script>

我很难复制这个。。。但是,如果在调用平台之后加载了很多js库(angular、moment、bootstrap),则不会触发onload回调。

下面是一个gif,显示console.log仅在刷新十几次后的一段时间内启动: https://i.imgur.com/C5FFJhb.gif

此html导致以下问题:

<script src="https://apis.google.com/js/platform.js?onload=platform_callback" async defer></script> 
<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.7.5/angular.js" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.7.5/angular-animate.js" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.7.5/angular-route.js" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.7.5/angular-sanitize.js" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js" crossorigin="anonymous"></script>
<script>
    function platform_callback() {
        console.log("init");
        gapi.load('auth2', function() {
            console.log("auth2");
        });
    }
</script>