Multi step

I am having a problem with a script base multi-step WPT test.

It seems fine to me when its single page WPT.

But, when that page included by a script, that page shows me a sort of error code like 503 403.

What’s the difference between those tests? Or Can I just ignore those error codes?

https://www.webpagetest.org/result/200616_KB_596a8510358d1870d494cc0bf3ce1797/1/details/#waterfall_view_step5

https://www.webpagetest.org/result/200616_9Q_60909b91ba4dbc8a064f04ebe1d799a3/1/details/#waterfall_view_step1