N/A First Byte Time - Dulles, VA 2017 iPad iOS 13

When we run our page speed test, we get a score of “N/A” for “First Byte Time”.


Is this a “divide by 0” bug because the First Byte time is 0.000s?

A different page on our site takes slightly longer to render on the server, but otherwise uses the same application stack, but it receives an “A” score:


Just trying to get a handle on how this is calculated and what is causing the difference.



Should be better now with the iOS 14 roll-out last night: https://www.webpagetest.org/result/200922_R1_6fc6949c40ef2b444d5e318550c2ecbf/

iOS 13 was racy with the beginning of a page load (The web inspector would only be able to attach after the navigation started). That was fixed with Safari in iOS 14 so it should be better now and always capture the start of the first request (which is needed for TTFB).