Thanks again for digging into this for me! This sounds very probable to be the issue here - I will fix this.That fixes it when I don't use the feature at all, yep.
Researching the other issue some more, I think I finally understand what's happening. The timer is incrementing when "inside" any target at all. Which includes the male's targets as well, his hand counts when holding his penis / masturbating. And there is only one timer. Correct solution would be to have separate timer for the male (incrementing on any "inside" state), and then for each female (incrementing only when penetrated). Although more detailed stimulation logic would be better than a simple timer of course.
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Regarding the simulation logic, I think that @hazmhox is working on a separate stimulation / intensity simulation plugin (as a replacement for vammoan's system), so I would rather link to this once its out (and hopefully a male voice in the new vammoan)!