so many veribles to this question as to give a true answer.
in truth if the net was rigged correctly and held up to the rabbts hitting it, it could for aguments sake hold 100% of the rabbits that ran into it.
if your asking how many could it hold before it began to allow rabbits to escape, again depends how its rigged, is it sown in, how much bagging 50 or 100% bagging ect ect.
Is there a maximum before it stops working? dont think there is but i have found nothing is ever set in stone regarding long nets. Like has ben said, a bit like asking how long is a piece of string but in my vi