@pipipipi for the community to assist you better please provide more details. You can mock/anonymize any sensitive information.
What is your current SPL, can you share some data? What is the drilldown code and behavior (does it run search in new window or set required token for drilldown panel search)?
Typically, although Single Value shows one value in the panel, its underlying search can be a time series data which is required to show the sparkline trend and only the latest value is displayed as the result. Also when we do drilldown to search without coding the tokens/values ourselves, it runs the underlying search which may give events from the previous pipe, hence return more results.