尽管页面上有ID，元素始终返回null

Question

<div id="parent">
<div id="content-wrap">
<div id="content" class="clearfix">                
<!-- 2019.1.215.45 -->
<div id="content-main-admin">
<div class="clearfix">
<div class="clearfix">
<div class="content-right">
<h1>Working Shift Manager
</h1>
<p>
Please find below all of your working shifts for administration.
</p>
</div>
</div>
<div class="clearfix">
<div class="content-right">
<div id="ctl00_cphContent_litAdminButtons" class="admin-buttons clearfix" 
style="margin: 0 0 20px 0">
<a href="working-shift-admin.aspx" class="button add" id="btnAdd" 
onclick="doSpinnerStart()">
Add New</a>

---

无法单击id元素btnAdd

public IWebElement AddNewButton { get { return FindByID("btnAdd"); } 

尝试从html读取

Element时，其返回为null，如果代码匹配，则我的代码将上面的值与html中的值进行比较，然后单击添加按钮。在这种情况下，将返回null且未单击按钮