Start Render getting triggered early by Chrome message?

Hi,
We have our own instance of web page test set up. I noticed our start render timings get triggered (possibly coincidentally) by Chrome’s “Waiting for [domain]…” message

Has anyone seen anything like this before?

Our actual page doesn’t have a gray background either, which also makes me suspicious of WPT.

Update your agents and both issues should go away: https://sites.google.com/a/webpagetest.org/docs/private-instances#TOC-Updating-Test-Agents