You can find the records which are included in the KPI by clicking on Show All Records below the KPI charts. If those records and KPI results seem to be mismatching, try REBUILD CACHE in CRM Sync settings.

Some KPIs, like Sales Won, has additional options such as Include dates in the future in Record selection for the behaviors.
Try changing the ON/OFF settings to see if the mismatch will be solved.

When your CRM org users have different timezones, KPI filter will show dates based on the earliest timezone of all users.

Check the conditions of KPI and if there are any customization/settings changes related to those conditions in CRM.
For example, user active/inactive, pick list value change, etc.

If all of the above does not work, try QUICK RE-SYNC for current month's data or FULL RE-SYNC for this year's data in CRM Sync settings.