What could explain discrepancies between USQL query results and custom metric data?

The first option highlights an essential factor when comparing USQL query results to custom metric data: the timeframe during which the data is collected. If the query timeframe differs from the timeframe for the custom metrics, this could lead to discrepancies in the data being analyzed. For instance, if a query is executed over a different range of time than that covered by the custom metrics, it may not include the same data points, resulting in apparent inconsistencies in the results. Aligning the timeframes ensures that both the queried data and the custom metrics refer to the same sampling period, allowing for accurate comparisons.

The other options do not account for this crucial aspect. While session inclusion and synthetic sessions can affect data on a more granular level, they do not universally explain discrepancies when the base timeframe itself is misaligned. Similarly, incorrect syntax in a query can indeed yield erroneous results, but this does not inherently relate to the comparison with a specific set of custom metrics regarding time alignment.