Email notifications are not being received

Hi, the email notifications (both notification and auto-responder) received are unreliable. Do you know what would cause this? Mostly the notifications work as normal, but two of my users have reported that some aren't coming through when they know they have submitted them. 

Also is it possible that a form could be submitted and then disappear? I have had one of my users reporting that they submitted a form, and then there is nothing in Submissions or no email notification/auto-responder.

Could the above problem (forms going missing) be due to user error or internet connectivity?

Are you referring to this form: http://www.jotform.co/form/41028727438861?

Since it has some upload fields in it if the internet connectivity is unstable or is lost at the moment of the submission then you won't be able to see it in the submissions screen since it wouldn't be completed.

I noticed that you're using multiple email addresses in the notifier of that form. Can you try to use only one to see if this is causing this behavior?

I've cleared your forms cache to see if this helps.