The fix is for the new reset option, there was an issue where the reset wasn't resetting the amount of time it takes for humans to turn once infected and they were all turning instantly on reset, oops! That is fixed now!
Other changes:

I've changed the max amount of time that people can be infected from 500 to 1000 and changed the default value from 250 to 500. I think having slower rates of infection will be making some of the upcoming updates more interesting.
The other change is that cars can now be destroyed when they hit too many civilians, they will no longer plow through infinite amounts. The current rule is there's a 20% chance the car will be destroyed when people get hit, I may consider allowing people to change that chance in the future.
I'm working on something I hope you'll find interesting in the upcoming weeks, but until then thanks for enjoying the game!
Changed files in this update