Sorry, that does sound very annoying. The game is heavily reliant on RNG, so it's possible that Nekos are spawning with Lust values low enough that they don't reach the point where they are extremely likely to start masturbating. Normally the answer would be to increase their Lust using potions, but since Neko Jizz is required for that it's not really a viable option early on.
I'll take another look at the math, and make sure that Nekos at least will always spawn with enough Lust to get to that point, since it's very annoying to not be able to kick off your file because of bad RNG like that.
Thanks so much for the information :3