Hello and welcome to the Conan Exile Forums.
Every time I encountered this problem, the purge attacked from the opposite side of the access door to the base.
The attackers therefore had to skirt the ramparts; They stopped their tracks along the way to attack the defenders located on the ramparts.
As a result, none arrived at the main gate of the base and the purge ended with the message “the attackers have not found the way”. Are you in the same situation?