When the end-user involves in a Virtual Agent(VA) conversation, the option to close the conversation at the top right corner of the VA client is disabled as shown in the below screenshot,
Release or Environment
Any latest release which supports Virtual Agent, from Newyork onwards.
Check in the topic by which topic is launched, if it is using "vaSystem.switchTopic()".
The "vaSystem.switchTopic()" is not documented and supported API.
The OOB topics are designed with "vaSystem.topicDiscovery()" API
Use supported "vaSystem.topicDiscovery()" API instead of "vaSystem.switchTopic()" API.
After changing the API, make sure that your updated topic is published.