Sequence contains more than one matching element

Hello!

I have a problem that has occurred after a migration from Epi v10.x.x to Epi v11.x.x and it only appears once I am logged in as an editor or admin to the site.

Navigation around the page as a visitor is working fine. But when navigating as an editor/admin our _footer.cshtml file throws an error. (See stack trace). Pretty much the same error appears if I try to navigate to /Cms/VisitorGroups or /EPiServer/AddOns view.

I have tried to reinstall all modules and packages and a lot of other stuff. Do you know what I can do? Or have any tips to push me in the right direction? Any help is appreciated

@{ var token = Html.GenerateAntiForgeryToken(Model.FeedbackForm); }

[InvalidOperationException: Sequence contains more than one matching element]
   System.Linq.Enumerable.SingleOrDefault(IEnumerable`1 source, Func`2 predicate) +370
   System.Web.Helpers.AntiXsrf.ClaimUidExtractor.GetUniqueIdentifierParameters(ClaimsIdentity claimsIdentity, String uniqueClaimTypeIdentifier) +156
   System.Web.Helpers.AntiXsrf.ClaimUidExtractor.ExtractClaimUid(IIdentity identity) +141
   System.Web.Helpers.AntiXsrf.TokenValidator.GenerateFormToken(HttpContextBase httpContext, IIdentity identity, AntiForgeryToken cookieToken) +215
   System.Web.Helpers.AntiXsrf.AntiForgeryWorker.GetTokens(HttpContextBase httpContext, AntiForgeryToken oldCookieToken, AntiForgeryToken& newCookieToken, AntiForgeryToken& formToken) +133
   System.Web.Helpers.AntiXsrf.AntiForgeryWorker.GetFormInputElement(HttpContextBase httpContext) +77
   System.Web.Helpers.AntiForgery.GetHtml() +148
   System.Web.Mvc.HtmlHelper.AntiForgeryToken() +28
   EPiServer.Forms.Internal.Security.AntiForgeryService.GenerateToken(HtmlHelper html, HttpContextBase httpContext, IFormContainerBlock formContainerBlock) +62
   EPiServer.Forms.Helpers.Internal.HtmlExtensions.GenerateAntiForgeryToken(HtmlHelper html, IFormContainerBlock formContainerBlock) +212
   ASP._Page_Views_Shared__Footer_cshtml.Execute() in C:\Projects\RiksTv\Web\rikstv.web\src\RiksTV.Web\Views\Shared\_Footer.cshtml:5
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +252
   System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +148
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +122
   StackExchange.Precompilation.PrecompilationView.Render(ViewContext viewContext, TextWriter writer) +148
   System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData) +136
   ASP._Page_Views__EdgeSkeleton_cshtml.Execute() in C:\Projects\RiksTv\Web\rikstv.web\src\RiksTV.Web\Views\_EdgeSkeleton.cshtml:39
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +252
   System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +148
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +122
   System.Web.WebPages.<>c__DisplayClass3.<RenderPageCore>b__2(TextWriter writer) +309
   System.Web.WebPages.WebPageBase.Write(HelperResult result) +108
   System.Web.WebPages.WebPageBase.RenderSurrounding(String partialViewName, Action`1 body) +89
   System.Web.WebPages.WebPageBase.PopContext() +310
   StackExchange.Precompilation.PrecompilationView.Render(ViewContext viewContext, TextWriter writer) +148
   System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +378
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +91
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +793
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +81
   System.Web.Mvc.Async.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult) +188
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +38
   System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +32
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +73
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +52
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +39
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +38
   System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState) +46
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +73
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +38
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +651
   System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +220
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +134

Sequence contains more than one matching element - AntiforgeryToken