AirNav have previously confirmed that only boxes actually sending data are shown on the map, so if it's quiet for aircraft showing position where you are, you won't show up.
Well, actually that can not be 100% true. Because my private Box Server based in Lehrte is Running 24/7 and sharing is activated. Usually it appears for about 1 or 2 days until it disappears from the map, even if there is traffic on my screen. Considering the fact, that I'm using an outdoor antenna with preamp giving me an average minimum range of 80nm, there is always some traffic to share in my range. Especially due to the fact that there is more or less no night-flight restriction at the bigger German Airports. Sorry, but from my point of view, I'm reckoning the map accuracy to be somewhere between the 5th or 6th basement floor, metaphorically speaking.
But maybe it could also be a problem with the RB Software itself, which could be based in the fact that it was never intended, that the Box software is running without any breaks.