This small cuckoo wasp, Trichrysis cyanea [1, 2] is a regular visitor of the bee hotels in the garden. The species is clearly a minority around the other Cuckoo wasp species and often only one specimen at the time is present.
Since the previous observation more specimen visit the bee hotels every year and they can be found elsewhere in the garden as well.
References1 Nederlands Soortenregister
2 PAUKKUNEN, Juho, et al. An illustrated key to the cuckoo wasps (Hymenoptera, Chrysididae) of the Nordic and Baltic countries, with description of a new species. ZooKeys, 2015, 548: 1.