The data that is available for analysis in the Power Automate Process Advisor is based on the data that is being logged for your flows. If a flow has not been run or has not been run recently, there will not be any data available for that flow in the Process Advisor.
Additionally, the data that is available for analysis is also based on the retention policy set for the data. The retention policy determines how long data is kept before it is purged.
If the retention policy is set to a shorter period, then the data will only be available for a shorter period of time.
It's also possible that the data available for some flows may have been deleted or removed by an administrator.
You can check the flow runs and their status for this particular flow in the Power Automate to check if there is any error that could have prevented the flow from running and also check if there is any filter set on the flow runs.
You can also check the retention policy in the Power Automate settings, to see if that's the reason of the data filter.
It is also worth noting that, if you are using Power Automate Premium, you can increase the retention period for the data in your tenant and also export the data to an external storage.