Cost Plan does not have the cost of the Resource Plan
These issues are happening due to the customization of your "ResourcePlan" Script Include.
Once reverted, I was no longer having issues.
To do so, follow the steps below.
1. Navigate to System Definition > Script Includes
2. In the "Name" column search for "ResourcePlan" and go to the record
3. In the Versions related list, Right-Click the record with the Source of "System Upgrades: VERSIONNAME..."
4. Select "Revert to this version"
5. Select OK when prompted