Scape and run: mod creatures such as parasites can directly cross the armor of the vehicle and attack the characters in the vehicle

Then this isn't a bug. Most vehicles don't have hitboxes to block mobs from attacking the player. Only a very few do, like tanks and AA vehicles.

Test: Scape and Run: Parasites

Do they physically move though the vehicle, or do they just attack you through it?

That doesn't make sense. Are you inside or outside the car?

But you said "If you attack me outside the car". That means you are outside the car and being attacked? Or are you inside the car, and the creature is outside the car, and they can attack you? If so, which car? Cause a lot of them don't have boxes to prevent attacks.

Which vehicle?

After testing with the mod, this is the conclusion:
depiction of what is happening, red are hitboxes

this is what was happening in the report
since to the ai, theres no obstacles in the way, so it has direct sight with the player

In conclusion, hitboxes are working correctly for armor. It's just that not all vehicles have said armor.