why have towers no effect on chip in cw?

on cw last night gmt+1 i tried to dps cora chip with my towers. i set up 5 of them and it showed the dmg on chip when they fireing. but it had no effect. I asked Archon % of ccc and it was 98% all the time. in this time the triple logged Mau´s from bells crashed down acc. So is it a Bug that...