Portal on one server:

test1
 
 <Custom Network OR Blank (Default) Network> #Verified for both.
 I

Portal on the other server:

test2
 
<same network as above> 
I

Interacting with the sign for these portals works as intended (i.e. network properly connects, displays correct destinations, etc).
Activating and teleporting through an interserver portal will send the user to the correct portal, but will fail to locate the desired exit location/portal (instead printing bungeeInvalidExitNetwork and sending the user to where they last logged off).