The first thing to check is how these duplicate devices are re-entering DCR. Alias resolution is not persistent. Once the aliases are resolved, the duplicate device is deleted. If that same device is brought back, then the alias will come back.
The way the RME alias algorithm work is as follows:
* Make sure the two devices have different DCR IDs (else they are really the same device).
* Find all entries in the RME database with the management IP address of the new device.
* For all matching interfaces, check the MAC address.
* If the MAC matches, check the port count on both devices.
* If all match, the device is an alias.