It seems like Amazon.EmailAddress slot type has trouble recognizing emails that end in 4 or more numbers. For example john2341@gmail.com. It just automatically switches to the next intent and asks for an email repeatedly again and again.
You can have your own regex in the Lambda code validation and assign it to the email slot if it passes your regex.
That's what I have done.
And you will be validating the email address anyway after getting it in a slot, so it's better to have your own regex.
Hope it helps.