Has the door collider been looked at, or was/is it one of the MF bugs?
I found it annoying/disappointing that in MMs hordenight vids, zombies glitched through the vault door every once a while, because there were so much of them outside, squeezing each other to the door.
By the way, it think it would be cool if lower tier doors (wood/scrap metal) had a chance to completely break off the hinges when a certain amount of zombies push against it (or single fat zombies like big mama or cop).
That would add some scary moments, when the door is blown through the room instead of slowly geeting damaged.
It could even be used by the player (maybe as perk/book) that you're able to enter a shed by running/crashing right through the closed front door...and then jump-escaping through the next window again because the shed is full of radiated sleepers