Head tags rendering in the body and BOM detected

In my solution, I have the tags inserted in the head. When I run the application, these tags are rendered inside the body.

I've also noticed that the browser detects BOM at the beginning of the body. If I comment the @Html.RenderWidget("Footer", "Index"); that is inside the footer, the application correctly renders the tags in the head and without the BOM.

 <footer>
    @Html.RenderWidget("Footer", "Index");
    @if (AbTesting.CheckVariant("sticky_phone_number_ski", "B"))
    {
        @Html.Partial("_CtaPanel")
    }
</footer>

There is my elements tab on browser

My WidgetHelper.cs looks like this

  public static class WidgetHelper
{
    public static MvcHtmlString RenderWidget(
        this HtmlHelper htmlHelper,
        string widgetName,
        string actionName = "",
        object parameters = null)
    {
        var widget = ReflectionHelper.GetAllWidgetControllers().SingleOrDefault(wdg => ReflectionHelper.GetWidgetName(wdg) == widgetName.ToLower());
        if (widget == null)
        {
            throw new Exception($"Widget with the name {widgetName} not found");
        }

        return RenderWidget(htmlHelper, widget, actionName, parameters);
    }

    public static MvcHtmlString RenderWidget(
        this HtmlHelper htmlHelper,
        Type widgetType,
        string actionName = "",
        object parameters = null)
    {
        try
        {
            var context = htmlHelper.ViewContext.HttpContext;
            if (widgetType == null)
            {
                throw new ArgumentNullException(nameof(widgetType));
            }

            if (context == null)
            {
                throw new ArgumentNullException(nameof(context));
            }

            var builder = new ControllerBuilder();
            var widgetName = ReflectionHelper.GetWidgetName(widgetType);
            var widgetController =
                builder.GetControllerFactory().CreateController(context.Request.RequestContext, widgetName) as
                WidgetController;
            if (widgetController == null)
            {
                return null;
            }

            if (string.IsNullOrEmpty(actionName))
            {
                actionName = widgetController.RouteData.GetRequiredString("Action");
            }

            var invoker = widgetController.ActionInvoker as WidgetActionInvoker;
            var action = invoker?.InvokeActionWithActionResult(widgetController.ControllerContext, actionName, parameters) as IWidgetResult;
            return action == null ? null : new MvcHtmlString(action.ResponseOutput.ToString());
        }
        catch (HttpException e)
        {
            throw e;
        }
        catch (Exception e)
        {
            LogManager.GetCurrentClassLogger().Error(e);
            return htmlHelper.ViewContext.HttpContext.Request.IsLocal ? new MvcHtmlString($"<p style='color: red'>Widget {widgetType?.FullName} has broken. Please see logs for more details.</p>") : null;
        }
    }
}

I have the same problem when I use others RenderWidget in the header. So I believe the problem is there.

Do you have any idea what could be causing this issue?