Nested comments don't work anymore for non registered users

Hi,

It looks like the plugin is interfering with the comment form in a strange way as it doesn’t let users that are not logged to answer a comment.
Answers from non logged users go straight down to the end of the comment list, as if they were new comments.

Any idea? Someone else experiencing the same problem?

https://wordpress.org/plugins/stop-spammer-registrations-plugin/