<? PHP tag in ajax response

I've deployed an application to Digital Ocean using Forge/Envoyer. Locally everything works fine. On the Digital Ocean server every ajax call responds with <?php prepended to the response. e.g. <?php{"data":{"id":6,"

Any clues? I've tried debugging but I'm not getting anything meaningful. The PHP side is using the following code:

    protected function respondWithItem($data, $transformer = null, $resourceKey = null)
    {
        return $this->respondWithArray($this->response->item($data, $transformer, $resourceKey));
    }

    protected function respondWithArray(array $array, array $headers = [])
    {
        $array = array_merge($array, ['meta' => $this->meta]);

        return response()->json($array, $this->statusCode, $headers);
    }

JavaScript Ajax handling is as follows:

(function() {
    $.ajaxSetup({
        headers: {
            'X-CSRF-TOKEN': $('meta[name="_token"]').attr('content')
        }
    });

    // Quickie PubSub
    var o = $({});
    $.subscribe = function() { o.on.apply(o, arguments) };
    $.unsubscribe = function() { o.off.apply(o, arguments) };
    $.publish = function() { o.trigger.apply(o, arguments) };

    // Async submit a form's input.
    var submitLaravelFormRequest = function(e) {
        var form = $(this);
        var method = form.find('input[name="_method"]').val() || 'POST';

        $.ajax({
            type: method,
            url: form.prop('action'),
            data: form.serialize(),
            success: function() {
                $.publish('ajax.formrequest.success', form);
                $.publish('ajax.request.success', form);
            }
        });

        e.preventDefault();
    };

    // Offer flash notification messages.
    // 'data-remote-success-message' => 'Yay. All Done.'
    $.subscribe('ajax.request.success', function(e, element) {
        var message = $(element).data('remote-success-message');

        if (message) {
            $('#flash').html('<div class="alert alert-success hidden-print">' + message + '</div>').fadeIn(300).delay(2500).fadeOut(300);
        }
    })

    // Handle success callbacks. To trigger Task.foo(), do:
    // 'data-model' => 'Task', 'data-remote-on-success' => 'foo'
    $.subscribe('ajax.formrequest.success', function(e, form) {
        triggerFormClickCallback.apply(form, [e, $(form).data('remote-on-success')]);
    });

    // Trigger the registered callback for a click or form submission.
    var triggerFormClickCallback = function(e, method) {
        var that = $(this);

        // What's the name of the parent model/scope/object.
        if ( ! (model = that.closest('*[data-model]').data('model'))) {
            return;
        }

        // As long as the object and method exist, trigger it and pass through the form.
        if (typeof window[model] == 'object' && typeof window[model][method] == 'function') {
            window[model][method](that);
        } else {
            console.error('Could not call method ' + method + ' on object ' + model);
        }

        e.preventDefault();
    }

    // Handle success callbacks. To trigger Task.foo(), do:
    // 'data-model' => 'Task', 'data-remote-on-success' => 'foo'
    $.subscribe('ajax.request.success', function(e, element) {
        triggerClickCallback.apply(element, [e, $(element).data('remote-on-success')]);
    });

    // Trigger the registered callback for a click or form submission.
    var triggerClickCallback = function(e, method) {
        var that = $(this);

        // As long as the object and method exist, trigger it and pass through the form.
        if (typeof window[method] == 'function') {
            window[method](that);
        } else {
            console.error('Could not call method ' + method );
        }

        e.preventDefault();
    }

    // Confirm an action before proceeding.
    var confirmAction = function(e) {
        var input = $(this);

        input.prop('disabled', 'disabled');

        bootbox.confirm(input.data('confirm'), function(result) {
            if (result == true){
                e.preventDefault();
                return true;
            }
        });

        input.removeAttr('disabled');

        return false;
    };

    // Dom bindings.
    $('form[data-remote]').on('submit', submitLaravelFormRequest);
    $('input[data-confirm], button[data-confirm]').on('click', confirmAction);
    $('*[data-click]').on('click', function(e) {
        triggerFormClickCallback.apply(this, [e, $(this).data('click')]);
    });
    //$('*[data-click-submits-form]').on('change', submitLaravelRequest);

    var displayPrintButton = function() {
        if (window.print) {
            document.write('<form><input type=button name=print value="Print" onClick="window.print()"></form>');
        }
    }

    // Async submit an ajax request.
    var submitLaravelRequest = function(e) {
        e.preventDefault();

        var element = $(this);
        var confirm = element.data('confirm');
        if (confirm !== undefined){
            bootbox.confirm(confirm, function(result) {
                if (result == true){
                    submitLaravelAjaxRequest(e, element);
                }
            });
        } else {
            submitLaravelAjaxRequest(e, element);
        }
    };

    var submitLaravelAjaxRequest = function(e, element) {
        var url = element.prop('href');
        var method = element.data('method') || 'POST';
        $.ajax({
            type: method,
            url: url,
            //data: form.serialize(),
            success: function() {
                //alert('SUCCESS');
                $.publish('ajax.request.success', element);
            },
            error: function onAjaxUpdateError (jqXHR, textStatus, errorThrown) {
                //alert(errorThrown); // TODO handle error
                $('#waitingModal').modal('hide');
                var errorModal = $('#errorModal');
                window.cloud9business.ajax.handleAjaxError(errorModal, jqXHR.responseJSON);
            }
        });
    };

    $('a[data-remote-click-submits], button[data-remote-click-submits]').on('click', submitLaravelRequest);

})();