MMM worker renaming and XID pool history
A worker name labels the origin of pool shares; it is not a hardware serial number. After a rename, the pool may retain the old label while new shares arrive under the new one. Two rows during that reporting window do not establish that two machines are mining.
What to check
Record the rename time and check the active MMM configuration: mainnet payout address, pool endpoint and new worker label. On that same pool, check whether the new label receives recent shares and the old label stops advancing. If both continue to submit fresh shares, investigate another running process or a second machine still using the old label. Do not diagnose duplication from a cached worker count alone.
Example
Example: mac becomes office-mac, but mac still shows an average hashrate. Check its last-share time before adding those averages together. Keep a single physical-device record in the overview where appropriate, and update the related project record rather than creating a second machine merely because its pool label changed.