Custom renderer doesn't work in iOS + library

I don't know why my Xamarin.Forms custom renderer doesn't work if I put it into a library and only on iOS, somebody could help me?

[assembly: ExportRenderer(typeof(HtmlLabel), typeof(HtmlLabelRenderer))]
namespace Plugin.HtmlLabel.iOS
{
    public class HtmlLabelRenderer : LabelRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<Label> e)
        {
            base.OnElementChanged(e);

            if (Control == null) return;
            UpdateMaxLines();
            UpdateText();
        }

It works fine on Android, UWP and iOS if into the project.

https://github.com/matteobortolazzo/HtmlLabelPlugin