For me they stopped spawning after 39. The only actions I did was place a lightning tower a couple kill back. (I replayed the game and did not have the same problem again.)
39 goes with the range as well. Hopefully overlapping the values will prevent it. I have yet to see it and others that I have shared the game with haven’t either but this is why a larger community is important :). Thanks for the info. I’m doing some clean up and adding a ‘boss’ and will include this with that release.