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.

Solution:

1.Browse Active Directory

2.Open Systems Management Container

3. Delete old record SMS-MP-site Code-machinename

4. Restart site server