at henesys hunting ground 1 the bottom floor it barely spawns any snails only 1 snail at a time i think.
Even though its not a bug, I have to say that I have noticed maps having a rather low spawn rate in places. Pig beach is the biggest example I can think of, I feel as if the spawn rate there is really slow. Also, I feel that this occurs in other maps as well. I can't give specific examples, but HHG1 has a certain slow feel to it, and so do many other places, FOG at times too.