How ArtNet-merge work on EN12

I have e probleme to merge 2 consoles via ArtNet.
2 grandma2 command wing, 1 4port switch - an 1 EN12.
port 1 is over ArtNet und i want to use the merger.
I tried with htp, ltp, DMX values at 0 at one console …
For some reasons, for seconds it works, that i can controll the lamp, but in the next moment, the lamp will have the old 0/0 value or doesn’t work?

How to merge 2 artnet oder Sacn signals? Or, not to unplug …