You failed to answer the question. Please go back and try another problem.

Can you provide any example page url for testing?

For Frank’s question, too often means it is still possible to submit sometimes?

Looks like the plugin can’t sent out any set-cookie header and have problem establish server-side session.

Can you checkout your PHP error log to see if there’s any warning?

I had designed a method to work with cookie-less client.
But in your case, it seems answers are not stored in session properly.

Maybe there’s something wrong with PHP session.

OK, I’m able to simulate the problem you have.

The conclusion now is:
1. the plugin cannot send session cookie on your website.
2. there’s something wrong with PHP’s session_id() to restore session without using cookie.

I’ll investigate and see if there’s a solution to this.