Overview
This audit ensures that the Google Publisher Tag (GPT) library is being loaded from the recommended host. The browser must open a connection to each new host your page references, which can take significant time. By loading GPT from the recommended host you ensure that all ad serving requests are made to a single domain, reducing the number of connections to open and improving page load performance.
Recommendations
Ensure that GPT is being loaded from securepubads.g.doubleclick.net. For
example:
<script async src="https://securepubads.g.doubleclick.net/tag/js/gpt.js"></script>
More information
Assessing Loading Performance in Real Life with Navigation and Resource Timing
Get Started with Google Publisher Tags