Not getting document complete value

Hi,

I using this site check page performance on desktop and mobile devices, works good for desktop but am not getting doc complete value for iPhone devices, below are the test link, could you please provide why it is happening and how can i fix this.

Test URL: https://www.webpagetest.org/result/190318_V7_f0925ddb918b5e0846120268127bbb7b/

-Naveen