Invalid source on Lowrance data source

[karlandnancy]

Here is my setup and issue

Hds 9 gen 3 at the helm with structure scan 3D
Hds 8 gen 2 at the back for back trolling networked through Ethernet cable to structure scan box.

Issue

When I go into data source on either unit for gps data, it makes the other unit on the network invalid and the gps doesn't work. I have this problem with other data such as water temp.

What is wrong and more importantly how do I fix it. I should be able to assign the data source independently on each unit with out affecting the other units.

Pm me with your number if you prefer