Virtual Agent Survey topic does not trigger after every single conversation. The occurrence of the topic after a conversation seems random.
Release or Environment
The system survey topic is referencing the 'com.glide.cs.survey.probability' system property to decide whether or not the post-chat survey should be displayed. Out of the box, this value is 0.33 which means it shows only 1/3 of the time.
If you want it to show every single time a conversation ends, go to sys_properties table and find the com.glide.cs.survey.probability property.
Set the value to 1.0
This will ensure that after every conversation the topic is called and displays the survey topic.