It is possible to clone comments with some limitations:
Comments and work logs with restricted visibility will not be cloned.
Deep Clone for Jira is able to clone user values between Jira instances, if the Jira user is available in both instances and connected to the same email address.
What happens if a Jira user is not available in the target instance?
If the reporter is not available in the target instance, Deep Clone sets the user who performed the clone as reporter.
If the assignee is not available in the target instance, Deep Clone sets the default assignee in the clone.
If the commenter is not available as a user, the creator of the comment is “Deep Clone for Jira”. A web-link to the user of the original issue in the source instance is provided, to track who originally created the comment.
If you clone a comment with @ mention the user will be displayed as “unknown user” or “user”.