There have been users who have experienced forms not working on their client sites, but working fine in development or on other servers.
There are various possibilities why this might happen and it happenned to me yesterday and I was scratching my head.
The website worked fine, the form thinks the email is sent but nothing appears. What can it be? PHP is fine.
Turns out the email forwarder for the hosting plan would not forward an email if the hosting account had no email address set up as part of the hosting. Once I did that the form posts started working.
A very silly thing to consider when installing a website on a new hosting plan.