Switching seats attacked by zombie.

[BobbyDisastrous]

If you switch seats within your car zombies can land attacks while you are switching. My car window wasn't open since I checked immediately afterwards. Be safe out there survivors

[BobbyDisastrous]

Alternatively it could have been this
https://old.reddit.com/r/projectzomboid/comments/w3lsgi/warning_theres_a_bug_which_allows_zombies_to/
If you enter and exit your car too many times you apparently lose the protection of your windows, I did get in and out of my car many times since I was trying to hitch a trailer to my van. Tragic way to go out

[BobbyDisastrous]

Door also might not have been closed, since if you drive immediately after entering the car, the door will not close..
https://theindiestone.com/forums/index.php?/topic/56827-4173-singleplayermultiplayer-vehicle-doors-not-closing-after-entering/

[Pherdnut]

So none of your windows were open? Didn't smash one on the passenger side to hotwire a survivor car?

[BobbyDisastrous]

No, everything was closed.

[martindirt]

Originally posted by adventureinc:

Door also might not have been closed, since if you drive immediately after entering the car, the door will not close..
https://theindiestone.com/forums/index.php?/topic/56827-4173-singleplayermultiplayer-vehicle-doors-not-closing-after-entering/

You can mark this as answer to your (not) question.
Make sure you hear the sound of the closing door.
TIS also planning to add animation to car doors opened / closed (like many modders already made it).