Depending on how you have things setup, and whether you are allowing your scenes to cross fade, you may want to read about the 'mode' input of the Matrix Value Receive actor. It deals with how values for matching inputs are handled.

I could think of a 'doubling' of the ArtNet stream. I'm not an expert on this protocol, but as it is based on UDP without any bit checking or correction, in oppsit to TCP. Therefore I could imagine, that the scenes overlaping two DMX value streams, creating some strange data pattern to be interpreted by the lights. Which means @wolands solution would indeed be preventing this. If you like to be sure about this, you might just put the separate ArtNet actors, as is into one scene and have a look what happens.

If you're not already using a background Scene, you may want to try that. Please see the TroikaTronix Youtube tutorial on activating multiple Scenes in Isadora.

Best wishes,

Woland