Q:

XML Deserializing returns "some" null values

Here's my XML:
<Events>
  <Event>
    <content_id>6442452774</content_id>
    <content_title>Title of the event</content_title>
    <content_html>
<Date>2015-11-18</Date>
<EventType>Events</EventType>
<Description>
<p>this is an "event"</p>
</Description>
<Speakers>speaker1 LLC<br />speaker2<br />Jspeaker3</Speakers>
<Time>5:30 - 6:00pm Registration<br />6:00 - 7:00pm Panel Discussion<br />7:00 - 8:00pm Networking Reception</Time>
<Where></Where>
<RegistrationInfo>Please contact <a href="mailto:events@events.com">events@events.com</a> to register for this event.</RegistrationInfo>
<Registration>false</Registration>
</content_html>
    <date_created>2015-10-24T14:24:12.333</date_created>
    <folder_id>262</folder_id>
    <content_teaser>this is the content "can you display it."</content_teaser>
    <content_text>text of the vent "more text" a lot of text here </content_text>
    <end_date>2015-11-19T21:35:00</end_date>
    <content_type>1</content_type>
    <template_id>43</template_id>
    <content_status>A</content_status>
  </Event>
<Event>.... Other events   </Event>
<Events>

and here's are my classes:
 public class Serializable_Events
    {
        [XmlElement("Event")]
        public List<Serializable_Event> EventList = new List<Serializable_Event>();
    }
    public class Serializable_Event
    {
        [XmlElement("content_id")]
        public string content_id { get; set; }

        [XmlElement("content_title")]
        public string content_title { get; set; }

        [XmlElement("content_html")]
        public Serializable_Event_ContentHTML ContentHTML { get; set; }
        [XmlText]
        public string content_teaser { get; set; }
        [XmlElement("content_text")]
        public string content_text { get; set; }
    }
    public class Serializable_Event_ContentHTML
    {
        [XmlElement("Date")]
        public string Date { get; set; }

        [XmlElement("EventType")]
        public string EventType { get; set; }

        [XmlElement("Description")]
        public string Description { get; set; }
        [XmlElement("Speakers")]
        public string Speakers { get; set; }

        [XmlElement("Time")]
        public string Time { get; set; }

        [XmlElement("Where")]
        public string Where { get; set; }

        [XmlElement("RegistrationInfo")]
        public string RegistrationInfo { get; set; }

        [XmlElement("Registration")]
        public bool Registration { get; set; }

        //ignored html tags
        [XmlIgnore]
        public string p { get; set; }
        [XmlIgnore]
        public string br { get; set; }
        [XmlIgnore]
        public string a { get; set; }

    }

Implementation:
XmlSerializer ser = new XmlSerializer(typeof(Serializable_Events));
            var data = (Serializable_Events)ser.Deserialize(new StreamReader(@"events.xml"));

My problem is that some attributes are null and some are not (see the screenshot)

A:

The ones that are null, like <Description> are due to malformed
XML. 
You are storing HMTL directly in XML with text all over the place, and the serializer is not expecting that; further you are telling the serializer to ignore HTML tags using XmlIgnore which is intended for XML tags with properly formed XML. That's a wrong use of XmlIgnore

All XML which contains non-XML mark-up should be wrapped in CDATA sections; this will solve your problem. Further, you can remove all of the XmlIgnore code as well since it's not needed.

Your XML should look like this:
<Events>
    <Event>
        <content_id>6442452774</content_id>
        <content_title>Title of the event</content_title>
        <content_html>
            <Date>2015-11-18</Date>
            <EventType>Events</EventType>
            <Description>
                <![CDATA[<p>this is an ""event""</p>]]>
            </Description>
            <Speakers>
                <![CDATA[speaker1 LLC<br />speaker2<br />Jspeaker3]]>
            </Speakers>
            <Time>
                <![CDATA[5:30 - 6:00pm Registration<br />6:00 - 7:00pm Panel Discussion<br />7:00 - 8:00pm Networking Reception]]>
            </Time>
            <Where></Where>
            <RegistrationInfo>
                <![CDATA[Please contact <a href='mailto:events@events.com'>events@events.com</a> to register for this event.]]>
            </RegistrationInfo>
            <Registration>false</Registration>
        </content_html>
        <date_created>2015-10-24T14:24:12.333</date_created>
        <folder_id>262</folder_id>
        <content_teaser>this is the content 'can you display it.'</content_teaser>
        <content_text>text of the vent 'more text' a lot of text here </content_text>
        <end_date>2015-11-19T21:35:00</end_date>
        <content_type>1</content_type>
        <template_id>43</template_id>
        <content_status>A</content_status>
    </Event>
</Events>"

