3 of 5 slow site complaints came from one ISP and it turned out to be my CDN

Five complaints in a fortnight on my auto parts site, which is a lot when the normal number for a month is zero. Three of the five mentioned Cox and two of them sent a cox speed test site screenshot showing 620 down, as if that closed the matter. My first assumtion was that it was their end and I could quietly ignore all five of them.

It was not their end. Ran webpagetest from three cities and one of them, Phoenix, came back with 2.9s to first byte while the other two sat at 180ms. The cdn was routing that region into a pop that was having a bad week, and my origin sits in Amsterdam so the trip was long to strat with. The fix was not clever. I turned on the smart routing option for a month to see whether it moved anything, it did, that region dropped to 310ms, and when I turned it off again it went straight back up, so now I pay for it every month. What I took from the whole thing is that the person complaining is usually right about the symptom and almost always wrong about the cause, and their isp speed test is still worth asking for, if only because it tells you roughly where they are sitting.