FIRST BYTE TIME FAILED

[pokongku]

I ran a WebPageTest a week ago, got As in most everything except compress images.
I ran the test again today and to my dismay, First Byte Time was F.

Haven't done anything to the site.
How does this happen?

A week ago : https://www.webpagetest.org/result/160728_PC_34BN/
Today : https://www.webpagetest.org/result/160804_KC_1VDQ/

How to fix this problem?

[pmeenan]

Try several runs to see if it was an outlier but it looks like things on the back-end were a lot slower on the recent test. My guess is that a week ago, the page was in a server cache (like W3TC) and the recent test was from a case where the page wasn't in cache (maybe you or someone else visited it right before the test last week).