Asp.Net页面连续9次回发后重置，求排查方向

在VS 2022中使用IIS Express（Chrome浏览器）测试ASP.NET网站时，发现UpdatePanel内设置AutoPostBack=true的RadSearchBox，在连续选择10+项后，前9次回发能正常处理，第10次及之后页面出现重置现象：Page_PreLoad阶段ViewState为空，控件无法正常实例化。

为复现问题，在回调方法中添加3秒Thread.Sleep模拟耗时操作，无论休眠时长，均会在9次回发后触发失效。

已完成排查：

• ViewState大小仅128字节，无异常增长
• 线程池可用线程数变化不超过1，无资源耗尽迹象
• 请求大小正常，无超限情况

现咨询：Ajax、IIS Express或IIS本身是否存在连续回发次数限制？

用户控件（仅保留问题相关PageView） #

<%@ Control Language="C#" AutoEventWireup="true" %>
<td class='<%# TdClass %>'>
    <telerik:RadPageView ID="PV1" runat="server">
        some controls
    </telerik:RadMultiPage>
    <telerik:RadPageView ID="PV2" runat="server">
        some controls
    </telerik:RadMultiPage>

    <telerik:RadPageView ID="PV3" runat="server">
        <div style="width: 75px; float: left;"> 
            <asp:UpdatePanel ID="UP1" runat="server" >
                <ContentTemplate>
                    <telerik:RadSearchBox ID="Combo1" runat="server" Width="100%" DataTextField="Descr"
                        DataValueField="Id" ZIndex="7001" EmptyMessage="- nom -" ShowSelectItem="true"
                        SelectItemText="" ExpandAnimation-Type="None" CollapseAnimation-Type="None"
                        AutoPostBack="true" OnSelectedIndexChanged="Combo1_SelectedIndexChanged" >
                    </stm:STMRadSearchBox>
                </ContentTemplate>
            </asp:UpdatePanel>
       </div>
    </telerik:RadPageView>
</telerik:RadMultiPage>
</td>

protected void Combo1_SelectedIndexChanged(object sender, RadComboBoxSelectedIndexChangedEventArgs e)
{
    Thread.Sleep(3000);
}

生成用户控件列表的面板 #

<%@ Control Language="C#" AutoEventWireup="true" %>
<telerik:RadAjaxPanel ID="IIRAP" runat="server">
<div class="Content">
    <span id="tata"></span>
    <telerik:RadListView ID="LVI" runat="server" GroupItemCount="3" OnNeedDataSource="LVI_NeedDataSource"
        OnItemCreated="LVI_ItemCreated" OnPreRender="LVI_PreRender" Visible="<%# CanViewIntervenant %>">
        <LayoutTemplate>
            <table>
                <tr id="groupPlaceholder" runat="server">
                </tr>
            </table>
        </LayoutTemplate>
        <GroupTemplate>
            <tr>
                <uc:ICTL ID="itemPlaceholder" runat="server" />
            </tr>
        </GroupTemplate>
        <ItemTemplate>
            <uc:ICTL ID="ICTL1" runat="server" />
        </ItemTemplate>
        <EmptyItemTemplate>
            <th>
                &nbsp;</td>
                <td>
                    &nbsp;
                </td>
        </EmptyItemTemplate>
    </telerik:RadListView>
</div>
</telerik:RadAjaxPanel>

使用该面板的页面 #

<%@ Page Language="C#"  %>
<%@ Register Src="~/UserControl/Detail.ascx" TagPrefix="uc" TagName="Detail" %>
<asp:Content ID="Content2" ContentPlaceHolderID="MC" runat="server" style="height: 100%">
<div id="divPageContent">
    <asp:ValidationSummary ID="ValidationSummarySave" runat="server" ValidationGroup="Save" CssClass="errorSummary" Style="margin-top: 30px;" />
    <telerik:RadPanelBar ID="PD1" runat="server" Width="100%" ExpandMode="MultipleExpandedItems">
        <Items>
            <telerik:RadPanelItem Value='<%# RadPanelItemValue.Intervenants.ToString() %>' Text="Intervenants"
                Expanded="true">
                <Items>
                    <telerik:RadPanelItem>
                        <ItemTemplate>
                            <uc:Detail ID="II1" runat="server" />
                        </ItemTemplate>
                    </telerik:RadPanelItem>
                </Items>
            </telerik:RadPanelItem>
        </Items>
    </telerik:RadPanelBar>
</div>
</asp:Content>

内容的提问来源于stack exchange，提问作者Eric Plante