I encountered the problem when running af side-by-side migration (ConfigMgr to Configmgr)
I had both management points in Active directory
Bascialliy it will happen when you deploy a new site site system with a new Management Point without removing old Management Point from System Container in Active Directory.
Error found in SMS_MP_CONTROL_MANAGER
MP has discarded a report when processing Ddr
Possible Cause: Corruption or invalid user definition.
Solution: Check the logs to identify the cause. If the problem is persistent raise the issue with Microsoft Support.
1.Browse Active Directory
2.Open Systems Management Container
3. Delete old record SMS-MP-site Code-machinename
4. Restart site server