提交按钮（asp.net mvc）在iOS9上不起作用

Question

在使用Html和asp.net MVC 5，javascript和jquery的网站中，我在登录表单中有一个提交按钮，当同时键入用户名和密码时，该按钮有效。在iOS 9.3的safari中键入用户名和psw时，无法验证此按钮。因此我无法单击“提交”按钮。它适用于iOS 10、11和12以及任何网络浏览器。

        <div class="containerw3layouts-agileits">
               @using (Html.BeginForm("Login", "Account", new { ReturnUrl = ViewBag.ReturnUrl }, FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
{
            @Html.AntiForgeryToken()
            @Html.ValidationSummary(true, "", new { @class = "text-danger" })
            <div class="form-group agileits-w3layouts">
                <div class="input-group" style="margin-top: 30px;">
                    <span class="input-group-addon"> <i class="glyphicon glyphicon-user"></i></span>

                    @Html.TextBoxFor(m => m.UserName, new { @class = "form-control agileinfo textbox", @placeholder = "Username", @style = "font-size: 12px;" })
                    @Html.ValidationMessageFor(m => m.UserName, "", new { @class = "text-danger" })
                </div>

            </div>

            <div class="form-group w3-agile password">
                <div class="input-group">
                    <span class="input-group-addon"><i class="glyphicon glyphicon-lock"></i> </span>
                    @Html.PasswordFor(m => m.Password, new { @class = "form-control agileinfo textbox", @placeholder = "Password", @style = "font-size: 12px;" })
                    @Html.ValidationMessageFor(m => m.Password, "", new { @class = "text-danger" })
                </div>

            </div>
                <div class="form-group w3-agile Button " style="text-align: center;margin-top:41px">
                <input id="loginbtn" type="submit" value="Log in" disabled class="btn btn-default btn-DD" style="width:124px;height:34px; background-color:#59C1DA; border:1px solid #5EB5D0;border-radius:3px;color:#fff;font-size:12px;line-height:14px;letter-spacing:.4px;font-family:Roboto" />
            </div>
        }
        </div>