When you wire something to XNET Create Session, there are two hidden terminals that can still be wired to at the bottom of the vi. You can connect a wire to the terminals, and (if you aren't using the auto-tool) you can start a wire from them - this differs slightly from the .NET Constructor issue (https://lavag.org/topic/20615-hidden-terminals-on-the-net-constructor-node/). Fortunately, the wires created from this are always broken, as the type of the terminals is void. The terminals are used for inputs in the Generic version of the Polymorphic VI, so you will need to start with a different version (I.e. the default Signal In Single-point that drops from the palettes).
The picture above has the wires coming out of the top, but the actual connection point is at the bottom (it is a 5-3-3-5 connector pane; these are the middle and left of the bottom 3).
I can reproduce this in LabVIEW 2015 SP1 with XNET 16.1, LabVIEW 2018 with XNET 17.0, and LabVIEW 2015 SP1 with XNET 18.0.0f1.