user.aspx has no definitions for SharingLinksGroupsDS

Today's YAP-day. Yet Another Problem...

I installed a few days ago an onPrem SharePoint Server 2016. After several good days and some updates, I get this error message when entering the /_layouts/user.aspx

Getting Error Message for Exception System.Web.HttpCompileException (0x80004005):
c:\Program Files\Common Files\microsoft shared\Web Server Extensions\16\TEMPLATE\LAYOUTS\user.aspx(506):
error CS1061: 'ASP._layouts_15_user_aspx' enthält keine Definition für 'SharingLinksGroupsDS_ObjectCreating', und es konnte keine Erweiterungsmethode 'SharingLinksGroupsDS_ObjectCreating' gefunden werden, die ein erstes Argument vom Typ 'ASP._layouts_15_user_aspx' akzeptiert (Fehlt eine Using-Direktive oder ein Assemblyverweis?).     bei
System.Web.Compilation.AssemblyBuilder.Compile()     bei
System.Web.Compilation.BuildProvidersCompiler.PerformBuild()     bei
System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath)     bei
System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)     bei
System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate)     bei
System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean throwIfNotFound)     bei
System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath virtualPath, Type requiredBaseType, HttpContext context, Boolean allowCrossApp)     bei
System.Web.UI.PageHandlerFactory.GetHandlerHelper(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath)     bei
System.Web.HttpApplication.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()     bei System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

I'm sorry that there's no english message but the clients server comes with the german language pack.

But maybe you know what's wrong with it? In line 506 (up to 510) I find this:

<asp:ObjectDataSource id="OrganizationEditSharingLinksDS" runat="server"
    OnObjectCreating="SharingLinksGroupsDS_ObjectCreating"
 TypeName="Microsoft.SharePoint.ApplicationPages.SharingLinksRolesDataSource,Microsoft.SharePoint.ApplicationPages,Version=16.0.0.0,Culture=neutral,PublicKeyToken=71e9bce111e9429c"
    SelectMethod="ListSharingLinksGroupUsers"
    FilterExpression="SharingLinkType = 'OrganizationEdit'" />

And before you ask: Of course we do NOT have any backup, because we're in the first configuration days so there's nothing productive on this machine.