What you observed is the expected behaviour for most MobiControl v13.x to v14.x server implementations.

In earlier implementations (v11 and before),  each Android device unique IMEI was used internally during device ernollment to avoid duplicate logical devices icon for the same device.  So, if an enrolled device was left factory-reset or disconnected from Mobicontrol by uninstalling the device agent while it was off-line,  the old device icon remained in the web-console and the MobiControl database.  If such device gets re-enrolled again to the same server, say even ten weeks later,  MobiControl compares the IMEI and will associate this same device to the old web-console entry, and no new Mobicontrol device license will be claimed.  As the device has been re-enrolled to the same logical device, checking its log entries  can also show all the log entries more than ten weeks before its re-enrollment.

On the contrary, the current v13/v14 implementations assigns  randomly generated device ID for each enrolled device. So, a re-enrolled device will have a new device icon  (and a new Mobicontrol device license claimed too)  co-existing with the old device icon in the web console.  In such case, you should manually remove the old device icon to free up the duplicate license claimed, as this old device icon will just be a zombie and never get connected and updated any more.   

Soti added back an option to enforce strict device ID checking during Android device re-enrollment in the latest v13.4 and v14.1.2 builds.   You can configure it in the item

  Enable re-enrollment    (for v13.4.x)

OR

  Enable Strict Android Re-Enrollment   (for v14.1.x)

at the bottom of  the tab "All Platforms->Servers->Global Settings->Enrollment Settings".

Hi Raymond,

thank you very much for your information.

I'll need to update MobiControl to the latest build then.

Do you also know, if devices that already got enrolled get a strict ID assigned to them for future re-enrollment after enabling Strict Android Re-Enrollment?

I am not 100% sure about what you mean in your question.  However,  with  Strict Android Re-Enrollment  selected, Mobicontrol server will try its best to associate a device with any existing icon with the same IMEI number (which is unique) during device enrollment.   So, a device's old (i.e. previously enrolled) icon needs not be located and deleted manually if such device need to be re-enrolled.

Thats pretty much the answer to my question.

Thank you again!