Hey,
sorry for the late reply, I had my fair share of issues with Vuforia, which delayed working on the network part.
It is just something I stumbled upon, when I did some UI debugging. I would've preferred an event to register to but your solution should most certainly work better than a fixed delay, thanks.
/edit
Unfortunately TNet.TNServerInstance.isActive does not fix my problem, since it is set true straight away when the Server is started. Like I wrote this seems like a threading issue. I will take a look at the example to see whether or not the issue is on my side (which it most likely is).
/edit2
Also breaks in the example.