Salesforce Opportunity Status Closed Won Shows Different Stages Within Reports

This behavior occurs, if the Opportunity Status value (such as "Closed Won") has not been mapped to the appropriate Type value. To map the values, please follow the below steps:

In Salesforce Classic:

1. Click Setup | Customize | Select Opportunity
2. Click on Fields
3. Click Stage 

4. Under the Opportunity Stages Picklist Values section, click edit to map the Stage Name with the correct Type.

5. Click Save.

In Lightning Experience:

1. Select Setup | Object Manager | Select Opportunity.
2. Click Fields & Relationships
3. Click Stage 
4. Under Opportunity Stages Picklist Values, Find the stage that shows different on the report. 
5. Click Edit.
6. Change the Type value and click Save.