Different scores are caused most often because the Google Lighthouse server is not located in the same place as ours, so the path that the data takes to reach the server can vary and this affects the speed.

When you run a speed test through Google Lighthouse in your browser, Lighthouse uses something called simulated throttling.
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With simulated throttling, the initial site speed data is collected on a fast connection. Based on this data, Lighthouse then estimates how quickly the page would have loaded on a different connection.

For example, if a page takes 2 seconds to render on a fast connection, Lighthouse might report a value of 6 seconds on a mobile device.
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Simulated throttling provides low variability and makes tests quick and cheap to run. However, it can also lead to inaccuracies, as Lighthouse doesn't fully replicate all browser features and network behaviors.
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To provide a score and report that better reflects how a real-world user (with a less-than-perfect computer and internet connection) would experience the page load, Monsido applies throttling when analyzing the web page through the Performance module. We’re basically interrupting the execution of CPU work at periodic intervals to emulate a slower processor.
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This approach leads to lower scores than when running Lighthouse in a browser, but the results are more realistic.
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If there is more load on the server.

Many users on the site, resulting in some lag or delay in the figures.

There is a backup of the workload on the server.