DP8000 Fixture Net/Artnet

Hi,
Maybe someone can offer some advice.
I have a small control package currently touring
01 x Full Boar 4 s/w 3.8.0.
02 x DP8000 s/w 3.8.0 (net number 3/4)
01 x unmanaged network switch

I've been having an ongoing issue when if i configure either of the external DP's.
I can get the DP's to output correctly up to and including 16 universes of Art-net each but when i try to configure
either DP with Art-net universes on two or more subnet's i get into difficulty.
So if all the universes are in for example subnet 7 then they work but if i have a single universe on subnet 8 i can't get the console to out put to that universe.

I am connecting the console to the network/DP's switch via Hog-Net using a static IP for each DP.
I am then using the fixture net port of the respective DP's to connect to the Artnet system.
I have disabled/switched off sAcn on the console and on both DP's.
I know the universes work correctly as i can patch/test them with 5-pin DMX and they work correctly.


Any suggestions or advice.
Thanks