Discovery is creating duplicate CI entries across multiple MID Servers

We have multiple MID Servers across different data centers. During a Discovery run, the same Windows server is being discovered by multiple MID Servers, resulting in duplicate cmdb_ci_computer records in CMDB.
The CMDB health score is dropping, and reconciliation is failing because the same CI has different serial_number or fqdn attributes populated inconsistently.

How do we identify the root cause and fix it so that Discovery stops creating duplicate CIs?