In your case it could be many things that caused the rabbits not to be in the net. Did you tail the nets? When rabbits hit the net at full speed they stretch the netting taught and unless their heads go through a mesh are unlikley to get caught at the first go, they usually bounce and then try again, or run along the net and if the net is not tailed they will escape.
When a rabbit is walked slowly into a net they usually try and push their way through a net, to do that they have to be standing on the net and that is when they get their claws tangled (especially with a double stranded net)