So Guilds are exploiting the ap system to "ambush" towers. They first acquire 100 ap, then all head to the top of a tower, making sure to attack no one to avoid losing ap. They then Rally at the top, with easy no way of the defenders being able to kick them out. They may camp up there a while, forcing people who may previously be guarding downstairs to come upstairs in case of a sudden attack, leaving the defenders vulnerable.

When they decide to attack, they may immediately lose their 100 ap, but it doesn't matter. They get a suprise attack with no warning time(it can happen at any given moment, for as long as they decide to wait), and they can quickly nuke down the hp of a tower very fast before people can react to the attack. If executed properly, a tower can fall in seconds to this tactic.

A simple fix to this would be to change the ap of people who enter a tower zone to 99 , so that they can't enter invincible and are immediately vulnerable. It's a zone intended for fighting, a player with no intent of fighting has no reason to be at a tower if they want to avoid pking.