I have a form I try to submit that can potentially have a lot of data and some users get a simple alert 'Undefined' when trying to submit. I've tried to replicate the issue on my local machine, on our test server and in production and I have no issues with all 3 environments.

I receive no error logs from our logging which leads me to think that it is an issue in the browser or front end since I would probably get a log message if it reached the backend.

...
<form id="WorkplaceIncidentForm" class="incidentReport text-center">
...
<button type="button" class="btn btn-info btn-lg" onclick="SendForm()">Submit</button>
...

function SendForm() {
   var form = $("#WorkplaceIncidentForm").serialize();
        var message = checkInputs();

        if (message === "valid") {
            $.ajax({
                type: "POST",
                url: "@Url.Action("Submit","Form")",
                data: form,
                dataType: 'json'
            })
                .fail(function (result) {
                    alert(result.message);
                })
                .done(function (result) {
                    if (result.success) {
                        alert('Successfully submitted!')
                        window.location.href = '../Form/ReportSubmitted';
                    }
                    else {
                        alert(result.message);
                    }
                });
        }
        else {
            alert('Please fill in ' + message + ' field.');
        }
}