There seems to be a bug regarding destroyed improvement within the war timeline. The war timeline always says, 0 improvements destroyed, even if one was really destroyed. Now, if you go to your notifications and view the attack from their, it will say that an improvement was destroyed.
For example, my timeline shows the follow text: "The attack destroyed 10.20 infrastructure in the city of DK Country and 0 improvements."
However, the same attack in my notifications section shows: "The attack destroyed 10.20 infrastructure in the city of DK Country. Leader Prapakaran stole $0.00 in the attack and destroyed 1 coalmine."
Hopefully I explained that well enough. If you need more details and further explanation, let me know.
Thanks!