Thanks for reporting.
After CueCore v1.53b & IoCore v1.16b the Art-Net actions became (almost) obsolete because the Art-Net & DMX action task did both write to the same (Show Control) buffer. In the IoCore there was a bug causing this buffer not being written to the Art-Net universe. In next version this will be fixed and the "GPI -> Art-Net" template will be removed as "GPI -> DMX" does the same thing.