Lab data and field data disagree. Trust the field data.
Run a performance test twice and you will often get two different numbers. Run it in two tools and you may get two different stories. This is not a bug in the tools. They are measuring different things.
Lab data
A single load, from one machine, on one connection, at one moment. Repeatable, controllable, and useful for comparing before and after a change.
Field data
What real people on real devices actually experienced, gathered by Google over weeks. Slower phones. Worse connections. A cold cache.
When they disagree
Believe the field data. Your lab test ran on a fast connection from a data centre. Your customer is on a phone, on mobile data, on a train.
Field data is also why some sites see no score for it at all: Google only reports it once there is enough traffic to be statistically meaningful. If your site is new, that section will say Skipped — not zero.
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