So, you have managed to get the desired behavior by resorting to a NonVisualTable, with client side filtering.
Ok. I hope that the data that gets filtered out is not too much, because this could pose scalability issues.

As far as I understand your new problem, we have never observed anything similar (but for the case that the Server is shut down).
Can you please provide us with a more detailed description of what happens?
What do you mean by "snapshot"? This word has a special meaning in Lightstreamer and I'm not sure if you mean a Lightstreamer snapshot or something else.