Webform still accepting submissions after form is closed

Hi, I have several webforms for event registrations runnning on a D7 site and I've never had an issue. However, with the latest event registration form I created, I seem to still be getting submissions from anonymous users even though the form was closed days ago. It was only a couple submissions, for a very popular event that was previously getting hundreds of submissions per day, so I think its appearing as closed for most people and I'm reaching out to the registrants who got through to see if they did anything special. But are there any known bugs that would explain this error? When I view the site in Safari, Chrome, or Firefox as an anonymous user, I do not see the form and I do see the "Submissions for this form are closed" alert. So how did these two registrants get in?

Is it possible that these two people had the form sitting open in a browser before it was closed, initiating a session, then that session let them override the closure of the form even though they submitted after the form was closed? This is the only explanation I could think of.

Thanks!!