To build this report do the following:
1. Go to the Report module.
2. Click on "+Add New".
3. Define the Entity Set to "Devices".
4. In the Propierties field add the "Label Count" operator.
5. In the Query operator add "COUNT (Labels) > 1"
Note: the query can also be used to know devices without labels by using the following Query operator "COUNT (Labels) = 0"
This should bring the expected information:

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Click To See Full Image.