Post back event does not fire after deployment

Question

I have a dropdown list with a selected index changed and auto postback set to true inside an update panel. The event fires when I run it on my machine. But after deployment and accessing it through the web, the event doesn't fire. Below is the snippet of my markup:

 

<div>
            <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                <ContentTemplate>
                    <asp:Timer ID="Timer1" runat="server"
                        Interval="240000" OnTick="Timer1_Tick">
                    </asp:Timer>
                    <div class="row">
                        <div class="col-lg-2">
                            Teacher's name:
                        </div>
                        <div class="col-lg-3">
                            <asp:DropDownList ID="ddlTeacherName" CssClass="form-control" DataTextField="FullName" DataValueField="TeacherID" runat="server" AutoPostBack="True" OnSelectedIndexChanged="ddlTeacherName_SelectedIndexChanged"></asp:DropDownList>
                        </div>
                        <div class="col-lg-2">
                            <asp:Label ID="lblTeacherID" runat="server" CssClass="form-control"></asp:Label>
                        </div>
                    </div>

                </ContentTemplate>
                <Triggers>
                    <asp:AsyncPostBackTrigger ControlID="Timer1" EventName="Tick" />
                </Triggers>
            </asp:UpdatePanel>
        </div>

Any help is very much appreciated.