AutoComplete Extender fills in IE11 but not in Chrome or Edge

[mellomel70]

I'm using Ajax Control Toolkit v20 in an ASP.Net 4 web page. Specifically, I'm using the AutoComplete Extender. It works fine in IE11 but when I run it in Chrome or Edge the list of items does not appear. The Service Method does fire and retrieve data, but no popup shows up. I've added z-index: 10000001; and position: relative; to each of the css classes I'm using for the extender, but the behavior doesn't change. Here's my front-end code:
`<asp:Panel ID="panelMatter" runat="server" CssClass="modalPopupAttorneys" align="center">

Select a Client / Matter Below <ajax:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server" TargetControlID="txtClient" MinimumPrefixLength="1" EnableCaching="true" CompletionSetCount="10" CompletionInterval="1000" ServiceMethod="GetClient" CompletionListCssClass="list2" CompletionListItemCssClass="listitem2" CompletionListHighlightedItemCssClass="hoverlistitem2"> </ajax:AutoCompleteExtender> <asp:Label ID="LblClient" runat="server" Width="595px" Text="Client"></asp:Label> <asp:TextBox ID="txtClient" runat="server" Width="600px" AutoPostBack="true" OnTextChanged="txtClient_TextChanged" Height="18px"></asp:TextBox> </td> </tr> <tr> <td><br /> <asp:Label ID="lblMatters" runat="server" Text="Matter(s)"></asp:Label> <div style="BORDER: thin solid; OVERFLOW: auto; WIDTH: 600px; HEIGHT: 300px"> <asp:CheckBoxList ID="lstMatters" runat="server" > </asp:CheckBoxList> </div> <asp:HiddenField ID="HiddenField1" runat="server" /> </td> </tr> </table>    ` And here's my server-side code: `[System.Web.Services.WebMethod] [System.Web.Script.Services.ScriptMethod()] public static List GetClient(string prefixText, int count) { String scommandtext = ""; if (Regex.IsMatch(prefixText, @"^\d+$")) { scommandtext = "SELECT ClientName,ClientNum FROM vw_ClientWithMatters WHERE ClientNum like '%" + prefixText + "%' "; } else { scommandtext = "SELECT ClientNum,ClientName FROM vw_ClientWithMatters WHERE ClientName like '%" + prefixText + "%' "; } DataTable dt = LHClassLibrary.LHDataAccessLayer.ExecuteSelect(scommandtext, false); List<string> ClientNames = new List<string>(); for (int i = 0; i < dt.Rows.Count; i++) { ClientNames.Add(dt.Rows[i][1].ToString()); } return ClientNames; }`