Our Lighthouse score dropped and nothing changed
It is almost always one of four things, and only one of them is your fault.
The score is a weighted composite of five metrics, measured on a throttled simulation, with a variance of several points between identical runs. A drop of four points is noise.
- Lighthouse updated. The weightings change between major versions.
- A third-party script got heavier. You did not change; your vendor did.
- The machine running it was busy. CI runners are shared.
- Something in your build genuinely grew. Check the bundle report before assuming this one.
Run it five times and take the median before you open a ticket.