RNG seed selection highly affects simulation otucomes

I'm developing for the first time a simulation in Omnet++ 5.4 that makes use of the queueinglib library available. In particular, I've built a simple model that comprehends a server and some passive queues.

I've repeated the simulation different times, setting different seeds and parameters, as written in the Omnet Simulation Manual, here is my omnetpp.ini:

# specify how many times a run needs to be repeated
repeat = 100
# default: different seed for each run
# seed-set = ${runnumber}
seed-set = ${repetition} # I tried both lines

OppNet.source.interArrivalTime = exponential(${10,5,2.5}s)

This produces 300 runs, 100 repetitions for each value of the interArrivalTime distribution parameter.

However, I'm observing some "strange" behaviour, namely, the resulting statistics are highly variable according to the RNG seed. For example, considering the lengths of the queues in my model, I have in the majority of the runs values smaller than 10, while in a few others a mean value that differs in orders of magnitude (85000, 45000?).

Does this mean that my implementation is wrong? Or is it possible that the random seed selection could influence the simulation outcomes so heavily?

Any help or hint is appreciated, thank you.