Citadel TC - single player

Today after many years I tried that single player map in which every player has citadel town centers and some tents, if you lose your TC you have only few seconds to rebuild it, or you're out. I am sure everybody already knows about this. But everytime I play it for maybe 15~20 minutes, my TC suddenly gets destroyed and I lose :/ even thought the timer is still there :D Why does this happen? I didn't have this problem with the original and Titans years ago.

Thank you in advance.