If walls are put to close together (aka Log Walls) they despawn after 10-12 hours. We had a perfectly built log wall with 29 walls built 6pm CET, now 7pm CET there are only 9 random walls left.

https://www.youtube.com/watch?v=iKDY3a304gI

It´s somewhat understandable that you dont want large bases on your servers because it gives lag, but it´s getting quite ridiculous now when it seems you do everything you can to make it easier to destroy bases and does nothing against the cheaters that destroys this game.