That's the main problem with precision issues. It's difficult to predict when or why it happens. In any case zooming in increases the probability that a pixels fetches the right color.
The fix is easy but needs more texture space: Add a transparent border to any image you provide. I could do that automatically for any plugins, let's see.
About the car count, I suspect you overload something if you want to spawn 100 cars immediately.
Per day at max one of your cars will be spawned. That might be a problem if no way is found or cars are disappearing more often than they spawn. Normally, no of your cars should disappear, but it happens if no way is found.