Are you saying that whenever a user selects a date in the datepicker, it wont save for that date field that the use selects but rather 1 day in the past ?
The field should retain its value as to what was set by the user and shouldn't change. Can you provide me with admin access to the site so that I can have a look as well as a link to the page here you have the form ?
I've enabled the private fields for your next response.
It would appear to be an issue with your plugins, unfortunately i'm not sure which one is causing the issue, however if you have a look at the form now. It now submits with the correct date information.
I would recommend re-enabling the plugins one at a time to see where it starts replicating the issue again.